ata: libata-scsi: fix ata_dsm_trim_pages() kernel-docgrafted

make htmldocs fails with:

  Documentation/driver-api/libata:604: ./drivers/ata/libata-scsi.c:2301:
  ERROR: Unexpected indentation. [docutils]

The Return: section of ata_dsm_trim_pages() ends its first sentence with
a colon and continues with an indented bullet list. reStructuredText
requires a blank line before an indented block, so docutils chokes on
the list.

Simply adding the missing blank line does not work either: Return: is a
kernel-doc "special section", which is terminated by the first blank
line, so the bullet list would end up in the Description section,
detached from the sentence introducing it.

Spell the two bounds out as prose instead, so that the Return: section
stays self-contained. Documentation-only change.

Fixes: e64e6b5dc867 ("ata: libata-scsi: scale DSM TRIM payload by MAX PAGES PER DSM COMMAND")
Reported-by: Thomas Huth <thuth@redhat.com>
Closes: https://lore.kernel.org/linux-ide/b0a0b8e8-cc4f-4c7b-8bc5-fee0712d405a@redhat.com/
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Link: https://lore.kernel.org/r/20260916130031.29990-2-cassel@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>

31 files changed, 4374 insertions, 0 deletions

diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore
new file mode 100644
index 000000000..9c9735570
--- /dev/null
+++ b/tools/testing/selftests/proc/.gitignore
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/fd-001-lookup
+/fd-002-posix-eq
+/fd-003-kthread
+/proc-2-is-kthread
+/proc-fsconfig-hidepid
+/proc-loadavg-001
+/proc-maps-race
+/proc-multiple-procfs
+/proc-net-dev-lseek
+/proc-empty-vm
+/proc-pid-vm
+/proc-self-map-files-001
+/proc-self-map-files-002
+/proc-self-isnt-kthread
+/proc-self-syscall
+/proc-self-wchan
+/proc-subset-pid
+/proc-tid0
+/proc-uptime-001
+/proc-uptime-002
+/proc-pidns
+/read
+/self
+/setns-dcache
+/setns-sysvipc
+/thread-self
diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile
new file mode 100644
index 000000000..a7de2bb6d
--- /dev/null
+++ b/tools/testing/selftests/proc/Makefile
@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: GPL-2.0-only
+CFLAGS += -Wall -O2 -Wno-unused-function
+CFLAGS += $(TOOLS_INCLUDES)
+LDFLAGS += -pthread
+
+TEST_GEN_PROGS :=
+TEST_GEN_PROGS += fd-001-lookup
+TEST_GEN_PROGS += fd-002-posix-eq
+TEST_GEN_PROGS += fd-003-kthread
+TEST_GEN_PROGS += proc-2-is-kthread
+TEST_GEN_PROGS += proc-loadavg-001
+TEST_GEN_PROGS += proc-maps-race
+TEST_GEN_PROGS += proc-net-dev-lseek
+TEST_GEN_PROGS += proc-empty-vm
+TEST_GEN_PROGS += proc-pid-vm
+TEST_GEN_PROGS += proc-self-map-files-001
+TEST_GEN_PROGS += proc-self-map-files-002
+TEST_GEN_PROGS += proc-self-isnt-kthread
+TEST_GEN_PROGS += proc-self-syscall
+TEST_GEN_PROGS += proc-self-wchan
+TEST_GEN_PROGS += proc-subset-pid
+TEST_GEN_PROGS += proc-tid0
+TEST_GEN_PROGS += proc-uptime-001
+TEST_GEN_PROGS += proc-uptime-002
+TEST_GEN_PROGS += read
+TEST_GEN_PROGS += self
+TEST_GEN_PROGS += setns-dcache
+TEST_GEN_PROGS += setns-sysvipc
+TEST_GEN_PROGS += thread-self
+TEST_GEN_PROGS += proc-multiple-procfs
+TEST_GEN_PROGS += proc-fsconfig-hidepid
+TEST_GEN_PROGS += proc-pidns
+
+include ../lib.mk
diff --git a/tools/testing/selftests/proc/config b/tools/testing/selftests/proc/config
new file mode 100644
index 000000000..68fbd2b35
--- /dev/null
+++ b/tools/testing/selftests/proc/config
@@ -0,0 +1 @@
+CONFIG_PROC_FS=y
diff --git a/tools/testing/selftests/proc/fd-001-lookup.c b/tools/testing/selftests/proc/fd-001-lookup.c
new file mode 100644
index 000000000..60d7948e7
--- /dev/null
+++ b/tools/testing/selftests/proc/fd-001-lookup.c
@@ -0,0 +1,168 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test /proc/*/fd lookup.
+
+#undef NDEBUG
+#include <assert.h>
+#include <dirent.h>
+#include <errno.h>
+#include <limits.h>
+#include <sched.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "proc.h"
+
+/* lstat(2) has more "coverage" in case non-symlink pops up somehow. */
+static void test_lookup_pass(const char *pathname)
+{
+	struct stat st;
+	ssize_t rv;
+
+	memset(&st, 0, sizeof(struct stat));
+	rv = lstat(pathname, &st);
+	assert(rv == 0);
+	assert(S_ISLNK(st.st_mode));
+}
+
+static void test_lookup_fail(const char *pathname)
+{
+	struct stat st;
+	ssize_t rv;
+
+	rv = lstat(pathname, &st);
+	assert(rv == -1 && errno == ENOENT);
+}
+
+static void test_lookup(unsigned int fd)
+{
+	char buf[64];
+	unsigned int c;
+	unsigned int u;
+	int i;
+
+	snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd);
+	test_lookup_pass(buf);
+
+	/* leading junk */
+	for (c = 1; c <= 255; c++) {
+		if (c == '/')
+			continue;
+		snprintf(buf, sizeof(buf), "/proc/self/fd/%c%u", c, fd);
+		test_lookup_fail(buf);
+	}
+
+	/* trailing junk */
+	for (c = 1; c <= 255; c++) {
+		if (c == '/')
+			continue;
+		snprintf(buf, sizeof(buf), "/proc/self/fd/%u%c", fd, c);
+		test_lookup_fail(buf);
+	}
+
+	for (i = INT_MIN; i < INT_MIN + 1024; i++) {
+		snprintf(buf, sizeof(buf), "/proc/self/fd/%d", i);
+		test_lookup_fail(buf);
+	}
+	for (i = -1024; i < 0; i++) {
+		snprintf(buf, sizeof(buf), "/proc/self/fd/%d", i);
+		test_lookup_fail(buf);
+	}
+	for (u = INT_MAX - 1024; u <= (unsigned int)INT_MAX + 1024; u++) {
+		snprintf(buf, sizeof(buf), "/proc/self/fd/%u", u);
+		test_lookup_fail(buf);
+	}
+	for (u = UINT_MAX - 1024; u != 0; u++) {
+		snprintf(buf, sizeof(buf), "/proc/self/fd/%u", u);
+		test_lookup_fail(buf);
+	}
+
+
+}
+
+int main(void)
+{
+	struct dirent *de;
+	unsigned int fd, target_fd;
+
+	if (unshare(CLONE_FILES) == -1)
+		return 1;
+
+	/* Wipe fdtable. */
+	do {
+		DIR *d;
+
+		d = opendir("/proc/self/fd");
+		if (!d)
+			return 1;
+
+		de = xreaddir(d);
+		assert(de->d_type == DT_DIR);
+		assert(streq(de->d_name, "."));
+
+		de = xreaddir(d);
+		assert(de->d_type == DT_DIR);
+		assert(streq(de->d_name, ".."));
+next:
+		de = xreaddir(d);
+		if (de) {
+			unsigned long long fd_ull;
+			unsigned int fd;
+			char *end;
+
+			assert(de->d_type == DT_LNK);
+
+			fd_ull = xstrtoull(de->d_name, &end);
+			assert(*end == '\0');
+			assert(fd_ull == (unsigned int)fd_ull);
+
+			fd = fd_ull;
+			if (fd == dirfd(d))
+				goto next;
+			close(fd);
+		}
+
+		closedir(d);
+	} while (de);
+
+	/* Now fdtable is clean. */
+
+	fd = open("/", O_PATH|O_DIRECTORY);
+	assert(fd == 0);
+	test_lookup(fd);
+	close(fd);
+
+	/* Clean again! */
+
+	fd = open("/", O_PATH|O_DIRECTORY);
+	assert(fd == 0);
+	/* Default RLIMIT_NOFILE-1 */
+	target_fd = 1023;
+	while (target_fd > 0) {
+		if (dup2(fd, target_fd) == target_fd)
+			break;
+		target_fd /= 2;
+	}
+	assert(target_fd > 0);
+	close(fd);
+	test_lookup(target_fd);
+	close(target_fd);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/fd-002-posix-eq.c b/tools/testing/selftests/proc/fd-002-posix-eq.c
new file mode 100644
index 000000000..417322ca9
--- /dev/null
+++ b/tools/testing/selftests/proc/fd-002-posix-eq.c
@@ -0,0 +1,57 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that open(/proc/*/fd/*) opens the same file.
+#undef NDEBUG
+#include <assert.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+int main(void)
+{
+	int fd0, fd1, fd2;
+	struct stat st0, st1, st2;
+	char buf[64];
+	int rv;
+
+	fd0 = open("/", O_DIRECTORY|O_RDONLY);
+	assert(fd0 >= 0);
+
+	snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd0);
+	fd1 = open(buf, O_RDONLY);
+	assert(fd1 >= 0);
+
+	snprintf(buf, sizeof(buf), "/proc/thread-self/fd/%u", fd0);
+	fd2 = open(buf, O_RDONLY);
+	assert(fd2 >= 0);
+
+	rv = fstat(fd0, &st0);
+	assert(rv == 0);
+	rv = fstat(fd1, &st1);
+	assert(rv == 0);
+	rv = fstat(fd2, &st2);
+	assert(rv == 0);
+
+	assert(st0.st_dev == st1.st_dev);
+	assert(st0.st_ino == st1.st_ino);
+
+	assert(st0.st_dev == st2.st_dev);
+	assert(st0.st_ino == st2.st_ino);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/fd-003-kthread.c b/tools/testing/selftests/proc/fd-003-kthread.c
new file mode 100644
index 000000000..dc591f97b
--- /dev/null
+++ b/tools/testing/selftests/proc/fd-003-kthread.c
@@ -0,0 +1,178 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that /proc/$KERNEL_THREAD/fd/ is empty.
+
+#undef NDEBUG
+#include <sys/syscall.h>
+#include <assert.h>
+#include <dirent.h>
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "proc.h"
+
+#define PF_KHTREAD 0x00200000
+
+/*
+ * Test for kernel threadness atomically with openat().
+ *
+ * Return /proc/$PID/fd descriptor if process is kernel thread.
+ * Return -1 if a process is userspace process.
+ */
+static int kernel_thread_fd(unsigned int pid)
+{
+	unsigned int flags = 0;
+	char buf[4096];
+	int dir_fd, fd;
+	ssize_t rv;
+
+	snprintf(buf, sizeof(buf), "/proc/%u", pid);
+	dir_fd = open(buf, O_RDONLY|O_DIRECTORY);
+	if (dir_fd == -1)
+		return -1;
+
+	/*
+	 * Believe it or not, struct task_struct::flags is directly exposed
+	 * to userspace!
+	 */
+	fd = openat(dir_fd, "stat", O_RDONLY);
+	if (fd == -1) {
+		close(dir_fd);
+		return -1;
+	}
+	rv = read(fd, buf, sizeof(buf));
+	close(fd);
+	if (0 < rv && rv <= sizeof(buf)) {
+		unsigned long long flags_ull;
+		char *p, *end;
+		int i;
+
+		assert(buf[rv - 1] == '\n');
+		buf[rv - 1] = '\0';
+
+		/* Search backwards: ->comm can contain whitespace and ')'. */
+		for (i = 0; i < 43; i++) {
+			p = strrchr(buf, ' ');
+			assert(p);
+			*p = '\0';
+		}
+
+		p = strrchr(buf, ' ');
+		assert(p);
+
+		flags_ull = xstrtoull(p + 1, &end);
+		assert(*end == '\0');
+		assert(flags_ull == (unsigned int)flags_ull);
+
+		flags = flags_ull;
+	}
+
+	fd = -1;
+	if (flags & PF_KHTREAD) {
+		fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);
+	}
+	close(dir_fd);
+	return fd;
+}
+
+static void test_readdir(int fd)
+{
+	DIR *d;
+	struct dirent *de;
+
+	d = fdopendir(fd);
+	assert(d);
+
+	de = xreaddir(d);
+	assert(streq(de->d_name, "."));
+	assert(de->d_type == DT_DIR);
+
+	de = xreaddir(d);
+	assert(streq(de->d_name, ".."));
+	assert(de->d_type == DT_DIR);
+
+	de = xreaddir(d);
+	assert(!de);
+}
+
+static inline int sys_statx(int dirfd, const char *pathname, int flags,
+			    unsigned int mask, void *stx)
+{
+	return syscall(SYS_statx, dirfd, pathname, flags, mask, stx);
+}
+
+static void test_lookup_fail(int fd, const char *pathname)
+{
+	char stx[256] __attribute__((aligned(8)));
+	int rv;
+
+	rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx);
+	assert(rv == -1 && errno == ENOENT);
+}
+
+static void test_lookup(int fd)
+{
+	char buf[64];
+	unsigned int u;
+	int i;
+
+	for (i = INT_MIN; i < INT_MIN + 1024; i++) {
+		snprintf(buf, sizeof(buf), "%d", i);
+		test_lookup_fail(fd, buf);
+	}
+	for (i = -1024; i < 1024; i++) {
+		snprintf(buf, sizeof(buf), "%d", i);
+		test_lookup_fail(fd, buf);
+	}
+	for (u = INT_MAX - 1024; u < (unsigned int)INT_MAX + 1024; u++) {
+		snprintf(buf, sizeof(buf), "%u", u);
+		test_lookup_fail(fd, buf);
+	}
+	for (u = UINT_MAX - 1024; u != 0; u++) {
+		snprintf(buf, sizeof(buf), "%u", u);
+		test_lookup_fail(fd, buf);
+	}
+}
+
+int main(void)
+{
+	unsigned int pid;
+	int fd;
+
+	/*
+	 * In theory this will loop indefinitely if kernel threads are exiled
+	 * from /proc.
+	 *
+	 * Start with kthreadd.
+	 */
+	pid = 2;
+	while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) {
+		pid++;
+	}
+	/* EACCES if run as non-root. */
+	if (pid >= 1024)
+		return 1;
+
+	test_readdir(fd);
+	test_lookup(fd);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-2-is-kthread.c b/tools/testing/selftests/proc/proc-2-is-kthread.c
new file mode 100644
index 000000000..f13668fb4
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-2-is-kthread.c
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2024 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test that kernel thread is reported as such. */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(void)
+{
+	/*
+	 * The following solutions don't really work:
+	 *
+	 * 1) jit kernel module which creates kernel thread:
+	 * test becomes arch-specific,
+	 * problems with mandatory module signing,
+	 * problems with lockdown mode,
+	 * doesn't work with CONFIG_MODULES=n at all,
+	 * kthread creation API is formally unstable internal kernel API,
+	 * need a mechanism to report test kernel thread's PID back,
+	 *
+	 * 2) ksoftirqd/0 and kswapd0 look like stable enough kernel threads,
+	 * but their PIDs are unstable.
+	 *
+	 * Check against kthreadd which always seem to exist under pid 2.
+	 */
+	int fd = open("/proc/2/status", O_RDONLY);
+	assert(fd >= 0);
+
+	char buf[4096];
+	ssize_t rv = read(fd, buf, sizeof(buf));
+	assert(0 <= rv && rv < sizeof(buf));
+	buf[rv] = '\0';
+
+	assert(strstr(buf, "Kthread:\t1\n"));
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-empty-vm.c b/tools/testing/selftests/proc/proc-empty-vm.c
new file mode 100644
index 000000000..b3f898aab
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-empty-vm.c
@@ -0,0 +1,541 @@
+#if defined __amd64__ || defined __i386__
+/*
+ * Copyright (c) 2022 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * Create a process without mappings by unmapping everything at once and
+ * holding it with ptrace(2). See what happens to
+ *
+ *	/proc/${pid}/maps
+ *	/proc/${pid}/numa_maps
+ *	/proc/${pid}/smaps
+ *	/proc/${pid}/smaps_rollup
+ */
+#undef _GNU_SOURCE
+#define _GNU_SOURCE
+
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/ptrace.h>
+#include <sys/resource.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#ifdef __amd64__
+#define TEST_VSYSCALL
+#endif
+
+#if defined __amd64__
+	#ifndef SYS_pkey_alloc
+		#define SYS_pkey_alloc 330
+	#endif
+	#ifndef SYS_pkey_free
+		#define SYS_pkey_free 331
+	#endif
+#elif defined __i386__
+	#ifndef SYS_pkey_alloc
+		#define SYS_pkey_alloc 381
+	#endif
+	#ifndef SYS_pkey_free
+		#define SYS_pkey_free 382
+	#endif
+#else
+	#error "SYS_pkey_alloc"
+#endif
+
+static int g_protection_key_support;
+
+static int protection_key_support(void)
+{
+	long rv = syscall(SYS_pkey_alloc, 0, 0);
+	if (rv > 0) {
+		syscall(SYS_pkey_free, (int)rv);
+		return 1;
+	} else if (rv == -1 && errno == ENOSYS) {
+		return 0;
+	} else if (rv == -1 && errno == EINVAL) {
+		// ospke=n
+		return 0;
+	} else {
+		fprintf(stderr, "%s: error: rv %ld, errno %d\n", __func__, rv, errno);
+		exit(EXIT_FAILURE);
+	}
+}
+
+/*
+ * 0: vsyscall VMA doesn't exist	vsyscall=none
+ * 1: vsyscall VMA is --xp		vsyscall=xonly
+ * 2: vsyscall VMA is r-xp		vsyscall=emulate
+ */
+static volatile int g_vsyscall;
+static const char *g_proc_pid_maps_vsyscall;
+static const char *g_proc_pid_smaps_vsyscall;
+
+static const char proc_pid_maps_vsyscall_0[] = "";
+static const char proc_pid_maps_vsyscall_1[] =
+"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0                  [vsyscall]\n";
+static const char proc_pid_maps_vsyscall_2[] =
+"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n";
+
+static const char proc_pid_smaps_vsyscall_0[] = "";
+
+static const char proc_pid_smaps_vsyscall_1[] =
+"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0                  [vsyscall]\n"
+"Size:                  4 kB\n"
+"KernelPageSize:        4 kB\n"
+"MMUPageSize:           4 kB\n"
+"Rss:                   0 kB\n"
+"Pss:                   0 kB\n"
+"Pss_Dirty:             0 kB\n"
+"Shared_Clean:          0 kB\n"
+"Shared_Dirty:          0 kB\n"
+"Private_Clean:         0 kB\n"
+"Private_Dirty:         0 kB\n"
+"Referenced:            0 kB\n"
+"Anonymous:             0 kB\n"
+"KSM:                   0 kB\n"
+"LazyFree:              0 kB\n"
+"AnonHugePages:         0 kB\n"
+"ShmemPmdMapped:        0 kB\n"
+"FilePmdMapped:         0 kB\n"
+"Shared_Hugetlb:        0 kB\n"
+"Private_Hugetlb:       0 kB\n"
+"Swap:                  0 kB\n"
+"SwapPss:               0 kB\n"
+"Locked:                0 kB\n"
+"THPeligible:           0\n"
+;
+
+static const char proc_pid_smaps_vsyscall_2[] =
+"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n"
+"Size:                  4 kB\n"
+"KernelPageSize:        4 kB\n"
+"MMUPageSize:           4 kB\n"
+"Rss:                   0 kB\n"
+"Pss:                   0 kB\n"
+"Pss_Dirty:             0 kB\n"
+"Shared_Clean:          0 kB\n"
+"Shared_Dirty:          0 kB\n"
+"Private_Clean:         0 kB\n"
+"Private_Dirty:         0 kB\n"
+"Referenced:            0 kB\n"
+"Anonymous:             0 kB\n"
+"KSM:                   0 kB\n"
+"LazyFree:              0 kB\n"
+"AnonHugePages:         0 kB\n"
+"ShmemPmdMapped:        0 kB\n"
+"FilePmdMapped:         0 kB\n"
+"Shared_Hugetlb:        0 kB\n"
+"Private_Hugetlb:       0 kB\n"
+"Swap:                  0 kB\n"
+"SwapPss:               0 kB\n"
+"Locked:                0 kB\n"
+"THPeligible:           0\n"
+;
+
+static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
+{
+	_exit(EXIT_FAILURE);
+}
+
+#ifdef TEST_VSYSCALL
+static void sigaction_SIGSEGV_vsyscall(int _, siginfo_t *__, void *___)
+{
+	_exit(g_vsyscall);
+}
+
+/*
+ * vsyscall page can't be unmapped, probe it directly.
+ */
+static void vsyscall(void)
+{
+	pid_t pid;
+	int wstatus;
+
+	pid = fork();
+	if (pid < 0) {
+		fprintf(stderr, "fork, errno %d\n", errno);
+		exit(1);
+	}
+	if (pid == 0) {
+		setrlimit(RLIMIT_CORE, &(struct rlimit){});
+
+		/* Hide "segfault at ffffffffff600000" messages. */
+		struct sigaction act = {};
+		act.sa_flags = SA_SIGINFO;
+		act.sa_sigaction = sigaction_SIGSEGV_vsyscall;
+		sigaction(SIGSEGV, &act, NULL);
+
+		g_vsyscall = 0;
+		/* gettimeofday(NULL, NULL); */
+		uint64_t rax = 0xffffffffff600000;
+		asm volatile (
+			"call *%[rax]"
+			: [rax] "+a" (rax)
+			: "D" (NULL), "S" (NULL)
+			: "rcx", "r11"
+		);
+
+		g_vsyscall = 1;
+		*(volatile int *)0xffffffffff600000UL;
+
+		g_vsyscall = 2;
+		exit(g_vsyscall);
+	}
+	waitpid(pid, &wstatus, 0);
+	if (WIFEXITED(wstatus)) {
+		g_vsyscall = WEXITSTATUS(wstatus);
+	} else {
+		fprintf(stderr, "error: vsyscall wstatus %08x\n", wstatus);
+		exit(1);
+	}
+}
+#endif
+
+static int test_proc_pid_maps(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/maps", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		perror("open /proc/${pid}/maps");
+		return EXIT_FAILURE;
+	} else {
+		ssize_t rv = read(fd, buf, sizeof(buf));
+		close(fd);
+		if (g_vsyscall == 0) {
+			assert(rv == 0);
+		} else {
+			size_t len = strlen(g_proc_pid_maps_vsyscall);
+			assert(rv == len);
+			assert(memcmp(buf, g_proc_pid_maps_vsyscall, len) == 0);
+		}
+		return EXIT_SUCCESS;
+	}
+}
+
+static int test_proc_pid_numa_maps(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/numa_maps", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT) {
+			/*
+			 * /proc/${pid}/numa_maps is under CONFIG_NUMA,
+			 * it doesn't necessarily exist.
+			 */
+			return EXIT_SUCCESS;
+		}
+		perror("open /proc/${pid}/numa_maps");
+		return EXIT_FAILURE;
+	} else {
+		ssize_t rv = read(fd, buf, sizeof(buf));
+		close(fd);
+		assert(rv == 0);
+		return EXIT_SUCCESS;
+	}
+}
+
+static int test_proc_pid_smaps(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/smaps", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT) {
+			/*
+			 * /proc/${pid}/smaps is under CONFIG_PROC_PAGE_MONITOR,
+			 * it doesn't necessarily exist.
+			 */
+			return EXIT_SUCCESS;
+		}
+		perror("open /proc/${pid}/smaps");
+		return EXIT_FAILURE;
+	}
+	ssize_t rv = read(fd, buf, sizeof(buf));
+	close(fd);
+
+	assert(0 <= rv);
+	assert(rv <= sizeof(buf));
+
+	if (g_vsyscall == 0) {
+		assert(rv == 0);
+	} else {
+		size_t len = strlen(g_proc_pid_smaps_vsyscall);
+		assert(rv > len);
+		assert(memcmp(buf, g_proc_pid_smaps_vsyscall, len) == 0);
+
+		if (g_protection_key_support) {
+#define PROTECTION_KEY "ProtectionKey:         0\n"
+			assert(memmem(buf, rv, PROTECTION_KEY, strlen(PROTECTION_KEY)));
+		}
+	}
+
+	return EXIT_SUCCESS;
+}
+
+static const char g_smaps_rollup[] =
+"00000000-00000000 ---p 00000000 00:00 0                                  [rollup]\n"
+"Rss:                   0 kB\n"
+"Pss:                   0 kB\n"
+"Pss_Dirty:             0 kB\n"
+"Pss_Anon:              0 kB\n"
+"Pss_File:              0 kB\n"
+"Pss_Shmem:             0 kB\n"
+"Shared_Clean:          0 kB\n"
+"Shared_Dirty:          0 kB\n"
+"Private_Clean:         0 kB\n"
+"Private_Dirty:         0 kB\n"
+"Referenced:            0 kB\n"
+"Anonymous:             0 kB\n"
+"KSM:                   0 kB\n"
+"LazyFree:              0 kB\n"
+"AnonHugePages:         0 kB\n"
+"ShmemPmdMapped:        0 kB\n"
+"FilePmdMapped:         0 kB\n"
+"Shared_Hugetlb:        0 kB\n"
+"Private_Hugetlb:       0 kB\n"
+"Swap:                  0 kB\n"
+"SwapPss:               0 kB\n"
+"Locked:                0 kB\n"
+;
+
+static int test_proc_pid_smaps_rollup(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/smaps_rollup", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT) {
+			/*
+			 * /proc/${pid}/smaps_rollup is under CONFIG_PROC_PAGE_MONITOR,
+			 * it doesn't necessarily exist.
+			 */
+			return EXIT_SUCCESS;
+		}
+		perror("open /proc/${pid}/smaps_rollup");
+		return EXIT_FAILURE;
+	} else {
+		ssize_t rv = read(fd, buf, sizeof(buf));
+		close(fd);
+		assert(rv == sizeof(g_smaps_rollup) - 1);
+		assert(memcmp(buf, g_smaps_rollup, sizeof(g_smaps_rollup) - 1) == 0);
+		return EXIT_SUCCESS;
+	}
+}
+
+static const char *parse_u64(const char *p, const char *const end, uint64_t *rv)
+{
+	*rv = 0;
+	for (; p != end; p += 1) {
+		if ('0' <= *p && *p <= '9') {
+			assert(!__builtin_mul_overflow(*rv, 10, rv));
+			assert(!__builtin_add_overflow(*rv, *p - '0', rv));
+		} else {
+			break;
+		}
+	}
+	assert(p != end);
+	return p;
+}
+
+/*
+ * There seems to be 2 types of valid output:
+ * "0 A A B 0 0 0\n" for dynamic exeuctables,
+ * "0 0 0 B 0 0 0\n" for static executables.
+ */
+static int test_proc_pid_statm(pid_t pid)
+{
+	char buf[4096];
+	snprintf(buf, sizeof(buf), "/proc/%u/statm", pid);
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		perror("open /proc/${pid}/statm");
+		return EXIT_FAILURE;
+	}
+
+	ssize_t rv = read(fd, buf, sizeof(buf));
+	close(fd);
+
+	assert(rv >= 0);
+	assert(rv <= sizeof(buf));
+
+	const char *p = buf;
+	const char *const end = p + rv;
+
+	/* size */
+	assert(p != end && *p++ == '0');
+	assert(p != end && *p++ == ' ');
+
+	uint64_t resident;
+	p = parse_u64(p, end, &resident);
+	assert(p != end && *p++ == ' ');
+
+	uint64_t shared;
+	p = parse_u64(p, end, &shared);
+	assert(p != end && *p++ == ' ');
+
+	uint64_t text;
+	p = parse_u64(p, end, &text);
+	assert(p != end && *p++ == ' ');
+
+	assert(p != end && *p++ == '0');
+	assert(p != end && *p++ == ' ');
+
+	/* data */
+	assert(p != end && *p++ == '0');
+	assert(p != end && *p++ == ' ');
+
+	assert(p != end && *p++ == '0');
+	assert(p != end && *p++ == '\n');
+
+	assert(p == end);
+
+	/*
+	 * "text" is "mm->end_code - mm->start_code" at execve(2) time.
+	 * munmap() doesn't change it. It can be anything (just link
+	 * statically). It can't be 0 because executing to this point
+	 * implies at least 1 page of code.
+	 */
+	assert(text > 0);
+
+	/*
+	 * These two are always equal. Always 0 for statically linked
+	 * executables and sometimes 0 for dynamically linked executables.
+	 * There is no way to tell one from another without parsing ELF
+	 * which is too much for this test.
+	 */
+	assert(resident == shared);
+
+	return EXIT_SUCCESS;
+}
+
+int main(void)
+{
+	int rv = EXIT_SUCCESS;
+
+#ifdef TEST_VSYSCALL
+	vsyscall();
+#endif
+
+	switch (g_vsyscall) {
+	case 0:
+		g_proc_pid_maps_vsyscall  = proc_pid_maps_vsyscall_0;
+		g_proc_pid_smaps_vsyscall = proc_pid_smaps_vsyscall_0;
+		break;
+	case 1:
+		g_proc_pid_maps_vsyscall  = proc_pid_maps_vsyscall_1;
+		g_proc_pid_smaps_vsyscall = proc_pid_smaps_vsyscall_1;
+		break;
+	case 2:
+		g_proc_pid_maps_vsyscall  = proc_pid_maps_vsyscall_2;
+		g_proc_pid_smaps_vsyscall = proc_pid_smaps_vsyscall_2;
+		break;
+	default:
+		abort();
+	}
+
+	g_protection_key_support = protection_key_support();
+
+	pid_t pid = fork();
+	if (pid == -1) {
+		perror("fork");
+		return EXIT_FAILURE;
+	} else if (pid == 0) {
+		rv = ptrace(PTRACE_TRACEME, 0, NULL, NULL);
+		if (rv != 0) {
+			if (errno == EPERM) {
+				fprintf(stderr,
+"Did you know? ptrace(PTRACE_TRACEME) doesn't work under strace.\n"
+				);
+				kill(getppid(), SIGTERM);
+				return EXIT_FAILURE;
+			}
+			perror("ptrace PTRACE_TRACEME");
+			return EXIT_FAILURE;
+		}
+
+		/*
+		 * Hide "segfault at ..." messages. Signal handler won't run.
+		 */
+		struct sigaction act = {};
+		act.sa_flags = SA_SIGINFO;
+		act.sa_sigaction = sigaction_SIGSEGV;
+		sigaction(SIGSEGV, &act, NULL);
+
+#ifdef __amd64__
+		munmap(NULL, ((size_t)1 << 47) - 4096);
+#elif defined __i386__
+		{
+			size_t len;
+
+			for (len = -4096;; len -= 4096) {
+				munmap(NULL, len);
+			}
+		}
+#else
+#error "implement 'unmap everything'"
+#endif
+		return EXIT_FAILURE;
+	} else {
+		/*
+		 * TODO find reliable way to signal parent that munmap(2) completed.
+		 * Child can't do it directly because it effectively doesn't exist
+		 * anymore. Looking at child's VM files isn't 100% reliable either:
+		 * due to a bug they may not become empty or empty-like.
+		 */
+		sleep(1);
+
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_maps(pid);
+		}
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_numa_maps(pid);
+		}
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_smaps(pid);
+		}
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_smaps_rollup(pid);
+		}
+		if (rv == EXIT_SUCCESS) {
+			rv = test_proc_pid_statm(pid);
+		}
+
+		/* Cut the rope. */
+		int wstatus;
+		waitpid(pid, &wstatus, 0);
+		assert(WIFSTOPPED(wstatus));
+		assert(WSTOPSIG(wstatus) == SIGSEGV);
+	}
+
+	return rv;
+}
+#else
+int main(void)
+{
+	return 4;
+}
+#endif
diff --git a/tools/testing/selftests/proc/proc-fsconfig-hidepid.c b/tools/testing/selftests/proc/proc-fsconfig-hidepid.c
new file mode 100644
index 000000000..b9af8f537
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-fsconfig-hidepid.c
@@ -0,0 +1,50 @@
+/*
+ * Copyright © 2020 Alexey Gladkov <gladkov.alexey@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <assert.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <linux/mount.h>
+#include <linux/unistd.h>
+
+static inline int fsopen(const char *fsname, unsigned int flags)
+{
+	return syscall(__NR_fsopen, fsname, flags);
+}
+
+static inline int fsconfig(int fd, unsigned int cmd, const char *key, const void *val, int aux)
+{
+	return syscall(__NR_fsconfig, fd, cmd, key, val, aux);
+}
+
+int main(void)
+{
+	int fsfd, ret;
+	int hidepid = 2;
+
+	assert((fsfd = fsopen("proc", 0)) != -1);
+
+	ret = fsconfig(fsfd, FSCONFIG_SET_BINARY, "hidepid", &hidepid, 0);
+	assert(ret == -1);
+	assert(errno == EINVAL);
+
+	assert(!fsconfig(fsfd, FSCONFIG_SET_STRING, "hidepid", "2", 0));
+	assert(!fsconfig(fsfd, FSCONFIG_SET_STRING, "hidepid", "invisible", 0));
+
+	assert(!close(fsfd));
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-loadavg-001.c b/tools/testing/selftests/proc/proc-loadavg-001.c
new file mode 100644
index 000000000..fb4fe9188
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-loadavg-001.c
@@ -0,0 +1,82 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test that /proc/loadavg correctly reports last pid in pid namespace. */
+#include <errno.h>
+#include <sched.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+int main(void)
+{
+	pid_t pid;
+	int wstatus;
+
+	if (unshare(CLONE_NEWPID) == -1) {
+		if (errno == ENOSYS || errno == EPERM)
+			return 4;
+		return 1;
+	}
+
+	pid = fork();
+	if (pid == -1)
+		return 1;
+	if (pid == 0) {
+		char buf[128], *p;
+		int fd;
+		ssize_t rv;
+
+		fd = open("/proc/loadavg" , O_RDONLY);
+		if (fd == -1)
+			return 1;
+		rv = read(fd, buf, sizeof(buf));
+		if (rv < 3)
+			return 1;
+		p = buf + rv;
+
+		/* pid 1 */
+		if (!(p[-3] == ' ' && p[-2] == '1' && p[-1] == '\n'))
+			return 1;
+
+		pid = fork();
+		if (pid == -1)
+			return 1;
+		if (pid == 0)
+			return 0;
+		if (waitpid(pid, NULL, 0) == -1)
+			return 1;
+
+		lseek(fd, 0, SEEK_SET);
+		rv = read(fd, buf, sizeof(buf));
+		if (rv < 3)
+			return 1;
+		p = buf + rv;
+
+		/* pid 2 */
+		if (!(p[-3] == ' ' && p[-2] == '2' && p[-1] == '\n'))
+			return 1;
+
+		return 0;
+	}
+
+	if (waitpid(pid, &wstatus, 0) == -1)
+		return 1;
+	if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0)
+		return 0;
+	return 1;
+}
diff --git a/tools/testing/selftests/proc/proc-maps-race.c b/tools/testing/selftests/proc/proc-maps-race.c
new file mode 100644
index 000000000..415eccb70
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-maps-race.c
@@ -0,0 +1,976 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2022 Google LLC.
+ * Author: Suren Baghdasaryan <surenb@google.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * Fork a child that concurrently modifies address space while the main
+ * process is reading /proc/$PID/maps and /proc/$PID/smaps, verifying the
+ * results. Address space modifications include:
+ *     VMA splitting and merging
+ *
+ */
+#define _GNU_SOURCE
+#include "kselftest_harness.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#define min(a, b) \
+	({ \
+		typeof(a) _a = (a); \
+		typeof(b) _b = (b); \
+		_a < _b ? _a : _b; \
+	})
+
+/* /proc/pid/maps parsing routines */
+struct page_content {
+	char *data;
+	ssize_t size;
+};
+
+#define LINE_MAX_SIZE		256
+
+struct line_content {
+	char text[LINE_MAX_SIZE];
+	unsigned long start_addr;
+	unsigned long end_addr;
+};
+
+enum test_state {
+	INIT,
+	CHILD_READY,
+	PARENT_READY,
+	SETUP_READY,
+	SETUP_MODIFY_MAPS,
+	SETUP_MAPS_MODIFIED,
+	SETUP_RESTORE_MAPS,
+	SETUP_MAPS_RESTORED,
+	TEST_READY,
+	TEST_DONE,
+};
+
+enum maps_file {
+	MAPS,
+	SMAPS,
+};
+
+struct vma_modifier_info;
+
+FIXTURE(proc_maps_race)
+{
+	struct vma_modifier_info *mod_info;
+	struct page_content page1;
+	struct page_content page2;
+	struct line_content last_line;
+	struct line_content first_line;
+	unsigned long duration_sec;
+	enum maps_file maps_file;
+	int shared_mem_size;
+	int skip_pages;
+	int page_size;
+	int vma_count;
+	bool verbose;
+	int maps_fd;
+	pid_t pid;
+};
+
+FIXTURE_VARIANT(proc_maps_race)
+{
+	const enum maps_file maps_file;
+};
+
+FIXTURE_VARIANT_ADD(proc_maps_race, maps) {
+	.maps_file = MAPS,
+};
+
+FIXTURE_VARIANT_ADD(proc_maps_race, smaps) {
+	.maps_file = SMAPS,
+};
+
+typedef bool (*vma_modifier_op)(FIXTURE_DATA(proc_maps_race) *self);
+typedef bool (*vma_mod_result_check_op)(struct line_content *mod_last_line,
+					struct line_content *mod_first_line,
+					struct line_content *restored_last_line,
+					struct line_content *restored_first_line);
+
+struct vma_modifier_info {
+	int vma_count;
+	void *addr;
+	int prot;
+	void *next_addr;
+	vma_modifier_op vma_modify;
+	vma_modifier_op vma_restore;
+	vma_mod_result_check_op vma_mod_check;
+	pthread_mutex_t sync_lock;
+	pthread_cond_t sync_cond;
+	enum test_state curr_state;
+	bool exit;
+	void *child_mapped_addr[];
+};
+
+static bool read_page(FIXTURE_DATA(proc_maps_race) *self,
+		      struct page_content *page)
+{
+	ssize_t  bytes_read;
+
+	bytes_read = read(self->maps_fd, page->data, self->page_size);
+	if (bytes_read <= 0)
+		return false;
+
+	/* Make sure data always ends with a newline character. */
+	if (page->data[bytes_read - 1] != '\n')
+		return false;
+
+	page->size = bytes_read;
+
+	return true;
+}
+
+static bool parse_vma_line(char *line_start, char *line_end,
+			   unsigned long *start, unsigned long *end)
+{
+	bool found;
+
+	*line_end = '\0'; /* stop sscanf at the EOL */
+	found = (sscanf(line_start, "%lx-%lx", start, end) == 2);
+	*line_end = '\n';
+
+	return found;
+}
+
+static int locate_containing_page(FIXTURE_DATA(proc_maps_race) *self,
+				  unsigned long addr, unsigned long size)
+{
+	unsigned long start, end;
+	int page = 0;
+
+	if (lseek(self->maps_fd, 0, SEEK_SET) < 0)
+		return -1;
+
+	while (true) {
+		char *curr_pos;
+		char *end_pos;
+
+		if (!read_page(self, &self->page1))
+			return -1;
+
+		curr_pos = self->page1.data;
+		end_pos = self->page1.data + self->page1.size;
+		while (curr_pos < end_pos) {
+			char *line_end;
+
+			line_end = strchr(curr_pos, '\n');
+			if (!line_end)
+				break;
+
+			if (parse_vma_line(curr_pos, line_end, &start, &end) &&
+			    start == addr && end == addr + size)
+				return page;
+
+			curr_pos = line_end + 1;
+		}
+		page++;
+	}
+
+	return 0;
+}
+
+static bool read_two_pages(FIXTURE_DATA(proc_maps_race) *self)
+{
+	if (lseek(self->maps_fd, 0, SEEK_SET) < 0)
+		return false;
+
+	for (int i = 0; i < self->skip_pages; i++)
+		if (!read_page(self, &self->page1))
+			return false;
+
+	return read_page(self, &self->page1) && read_page(self, &self->page2);
+}
+
+static void copy_line(const char *line_start, const char *line_end,
+		      char *buf, size_t buf_size)
+{
+	size_t len = min(line_end - line_start, buf_size - 1);
+
+	strncpy(buf, line_start, len);
+	buf[len] = '\0';
+}
+
+static void copy_first_line(struct page_content *page, char *first_line,
+			    size_t line_size)
+{
+	copy_line(page->data, strchr(page->data, '\n'), first_line, line_size);
+}
+
+static void copy_last_line(struct page_content *page, char *last_line,
+			   size_t line_size)
+{
+	/* Get the last line in the first page */
+	const char *end = page->data + page->size - 1;
+	/* skip last newline */
+	const char *pos = end - 1;
+
+	/* search previous newline */
+	while (pos[-1] != '\n')
+		pos--;
+
+	copy_line(pos, end, last_line, line_size);
+}
+
+static bool copy_first_entry(struct page_content *page, char *first_line,
+			     size_t line_size)
+{
+	char *start_pos = page->data;
+
+	while (start_pos < page->data + page->size) {
+		unsigned long start_addr;
+		unsigned long end_addr;
+		char *end_pos;
+
+		end_pos = strchr(start_pos, '\n');
+		if (!end_pos)
+			break;
+
+		if (parse_vma_line(start_pos, end_pos, &start_addr, &end_addr)) {
+			copy_line(start_pos, end_pos, first_line, line_size);
+			return true;
+		}
+
+		start_pos = end_pos + 1;
+	}
+
+	return false;
+}
+
+static bool copy_last_entry(struct page_content *page, char *last_line,
+			    size_t line_size)
+{
+	char *end_pos = page->data + page->size - 1;
+	char *start_pos;
+
+	while (end_pos > page->data) {
+		unsigned long start_addr;
+		unsigned long end_addr;
+
+		/* skip last newline */
+		start_pos = end_pos - 1;
+		/* search previous newline */
+		while (start_pos > page->data && start_pos[-1] != '\n')
+			start_pos--;
+		if (parse_vma_line(start_pos, end_pos, &start_addr, &end_addr)) {
+			copy_line(start_pos, end_pos, last_line, line_size);
+			return true;
+		}
+
+		end_pos = start_pos - 1;
+	}
+
+	return false;
+}
+
+/* Read the last line of the first page and the first line of the second page */
+static bool read_boundary_lines(FIXTURE_DATA(proc_maps_race) *self,
+				struct line_content *last_line,
+				struct line_content *first_line)
+{
+	if (!read_two_pages(self))
+		return false;
+
+	if (self->maps_file == MAPS) {
+		copy_last_line(&self->page1, last_line->text, LINE_MAX_SIZE);
+		copy_first_line(&self->page2, first_line->text, LINE_MAX_SIZE);
+	} else if (self->maps_file == SMAPS) {
+		if (!copy_last_entry(&self->page1, last_line->text, LINE_MAX_SIZE) ||
+		    !copy_first_entry(&self->page2, first_line->text, LINE_MAX_SIZE))
+			return false;
+	} else {
+		return false;
+	}
+
+	return sscanf(last_line->text, "%lx-%lx", &last_line->start_addr,
+		      &last_line->end_addr) == 2 &&
+	       sscanf(first_line->text, "%lx-%lx", &first_line->start_addr,
+		      &first_line->end_addr) == 2;
+}
+
+/* Thread synchronization routines */
+static void wait_for_state(struct vma_modifier_info *mod_info, enum test_state state)
+{
+	pthread_mutex_lock(&mod_info->sync_lock);
+	while (mod_info->curr_state != state)
+		pthread_cond_wait(&mod_info->sync_cond, &mod_info->sync_lock);
+	pthread_mutex_unlock(&mod_info->sync_lock);
+}
+
+static void signal_state(struct vma_modifier_info *mod_info, enum test_state state)
+{
+	pthread_mutex_lock(&mod_info->sync_lock);
+	mod_info->curr_state = state;
+	pthread_cond_signal(&mod_info->sync_cond);
+	pthread_mutex_unlock(&mod_info->sync_lock);
+}
+
+static void stop_vma_modifier(struct vma_modifier_info *mod_info)
+{
+	wait_for_state(mod_info, SETUP_READY);
+	mod_info->exit = true;
+	signal_state(mod_info, SETUP_MODIFY_MAPS);
+}
+
+static void print_first_lines(char *text, int nr)
+{
+	const char *end = text;
+
+	while (nr && (end = strchr(end, '\n')) != NULL) {
+		nr--;
+		end++;
+	}
+
+	if (end) {
+		int offs = end - text;
+
+		text[offs] = '\0';
+		printf("%s", text);
+		text[offs] = '\n';
+		printf("\n");
+	} else {
+		printf("%s", text);
+	}
+}
+
+static void print_last_lines(char *text, int nr)
+{
+	const char *start = text + strlen(text);
+
+	nr++; /* to ignore the last newline */
+	while (nr) {
+		while (start > text && *start != '\n')
+			start--;
+		nr--;
+		start--;
+	}
+	printf("%s", start);
+}
+
+static void print_boundaries(const char *title, FIXTURE_DATA(proc_maps_race) *self)
+{
+	if (!self->verbose)
+		return;
+
+	printf("%s", title);
+	/* Print 3 boundary lines from each page */
+	print_last_lines(self->page1.data, 3);
+	printf("-----------------page boundary-----------------\n");
+	print_first_lines(self->page2.data, 3);
+}
+
+static bool print_boundaries_on(bool condition, const char *title,
+				FIXTURE_DATA(proc_maps_race) *self)
+{
+	if (self->verbose && condition)
+		print_boundaries(title, self);
+
+	return condition;
+}
+
+static void report_test_start(const char *name, bool verbose)
+{
+	if (verbose)
+		printf("==== %s ====\n", name);
+}
+
+static struct timespec print_ts;
+
+static void start_test_loop(struct timespec *ts, bool verbose)
+{
+	if (verbose)
+		print_ts.tv_sec = ts->tv_sec;
+}
+
+static void end_test_iteration(struct timespec *ts, bool verbose)
+{
+	if (!verbose)
+		return;
+
+	/* Update every second */
+	if (print_ts.tv_sec == ts->tv_sec)
+		return;
+
+	printf(".");
+	fflush(stdout);
+	print_ts.tv_sec = ts->tv_sec;
+}
+
+static void end_test_loop(bool verbose)
+{
+	if (verbose)
+		printf("\n");
+}
+
+static bool capture_mod_pattern(FIXTURE_DATA(proc_maps_race) *self,
+				struct line_content *mod_last_line,
+				struct line_content *mod_first_line,
+				struct line_content *restored_last_line,
+				struct line_content *restored_first_line)
+{
+	print_boundaries("Before modification", self);
+
+	signal_state(self->mod_info, SETUP_MODIFY_MAPS);
+	wait_for_state(self->mod_info, SETUP_MAPS_MODIFIED);
+
+	/* Copy last line of the first page and first line of the last page */
+	if (!read_boundary_lines(self, mod_last_line, mod_first_line))
+		return false;
+
+	print_boundaries("After modification", self);
+
+	signal_state(self->mod_info, SETUP_RESTORE_MAPS);
+	wait_for_state(self->mod_info, SETUP_MAPS_RESTORED);
+
+	/* Copy last line of the first page and first line of the last page */
+	if (!read_boundary_lines(self, restored_last_line, restored_first_line))
+		return false;
+
+	print_boundaries("After restore", self);
+
+	if (!self->mod_info->vma_mod_check(mod_last_line, mod_first_line,
+					   restored_last_line, restored_first_line))
+		return false;
+
+	/*
+	 * The content of these lines after modify+resore should be the same
+	 * as the original.
+	 */
+	return strcmp(restored_last_line->text, self->last_line.text) == 0 &&
+	       strcmp(restored_first_line->text, self->first_line.text) == 0;
+}
+
+static bool query_addr_at(int maps_fd, void *addr,
+			  unsigned long *vma_start, unsigned long *vma_end)
+{
+	struct procmap_query q;
+
+	memset(&q, 0, sizeof(q));
+	q.size = sizeof(q);
+	/* Find the VMA at the split address */
+	q.query_addr = (unsigned long long)addr;
+	q.query_flags = 0;
+	if (ioctl(maps_fd, PROCMAP_QUERY, &q))
+		return false;
+
+	*vma_start = q.vma_start;
+	*vma_end = q.vma_end;
+
+	return true;
+}
+
+static inline bool split_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	/* PROT_NONE differs from both readable neighbors. */
+	return mmap(self->mod_info->addr, self->page_size, PROT_NONE,
+		    MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) != MAP_FAILED;
+}
+
+static inline bool merge_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	return mmap(self->mod_info->addr, self->page_size, self->mod_info->prot,
+		    MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) != MAP_FAILED;
+}
+
+static inline bool check_split_result(struct line_content *mod_last_line,
+				      struct line_content *mod_first_line,
+				      struct line_content *restored_last_line,
+				      struct line_content *restored_first_line)
+{
+	/* Make sure vmas at the boundaries are changing */
+	return strcmp(mod_last_line->text, restored_last_line->text) != 0 &&
+	       strcmp(mod_first_line->text, restored_first_line->text) != 0;
+}
+
+static inline bool shrink_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	return mremap(self->mod_info->addr, self->page_size * 3,
+		      self->page_size, 0) != MAP_FAILED;
+}
+
+static inline bool expand_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	return mremap(self->mod_info->addr, self->page_size,
+		      self->page_size * 3, 0) != MAP_FAILED;
+}
+
+static inline bool check_shrink_result(struct line_content *mod_last_line,
+				       struct line_content *mod_first_line,
+				       struct line_content *restored_last_line,
+				       struct line_content *restored_first_line)
+{
+	/* Make sure only the last vma of the first page is changing */
+	return strcmp(mod_last_line->text, restored_last_line->text) != 0 &&
+	       strcmp(mod_first_line->text, restored_first_line->text) == 0;
+}
+
+static inline bool remap_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	/*
+	 * Remap the last page of the next vma into the middle of the vma.
+	 * This splits the current vma and the first and middle parts (the
+	 * parts at lower addresses) become the last vma objserved in the
+	 * first page and the first vma observed in the last page.
+	 */
+	return mremap(self->mod_info->next_addr + self->page_size * 2, self->page_size,
+		      self->page_size, MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+		      self->mod_info->addr + self->page_size) != MAP_FAILED;
+}
+
+static inline bool patch_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	return mprotect(self->mod_info->addr + self->page_size, self->page_size,
+			self->mod_info->prot) == 0;
+}
+
+static inline bool check_remap_result(struct line_content *mod_last_line,
+				      struct line_content *mod_first_line,
+				      struct line_content *restored_last_line,
+				      struct line_content *restored_first_line)
+{
+	/* Make sure vmas at the boundaries are changing */
+	return strcmp(mod_last_line->text, restored_last_line->text) != 0 &&
+	       strcmp(mod_first_line->text, restored_first_line->text) != 0;
+}
+
+FIXTURE_SETUP(proc_maps_race)
+{
+	const char *verbose = getenv("VERBOSE");
+	const char *duration = getenv("DURATION");
+	struct vma_modifier_info *mod_info;
+	pthread_mutexattr_t mutex_attr;
+	pthread_condattr_t cond_attr;
+	unsigned long first_map_addr;
+	unsigned long last_map_addr;
+	unsigned long duration_sec;
+	char fname[32];
+
+	self->page_size = (unsigned long)sysconf(_SC_PAGESIZE);
+	self->verbose = verbose && !strncmp(verbose, "1", 1);
+	self->maps_file = variant->maps_file;
+	duration_sec = duration ? atol(duration) : 0;
+	self->duration_sec = duration_sec ? duration_sec : 5UL;
+
+	/*
+	 * Have to map enough vmas for /proc/pid/maps to contain more than one
+	 * page worth of vmas. Assume at least 32 bytes per line in maps output
+	 */
+	self->vma_count = self->page_size / 32 + 1;
+	self->shared_mem_size = sizeof(struct vma_modifier_info) + self->vma_count * sizeof(void *);
+
+	/* map shared memory for communication with the child process */
+	self->mod_info = (struct vma_modifier_info *)mmap(NULL, self->shared_mem_size,
+				PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+	ASSERT_NE(self->mod_info, MAP_FAILED);
+	mod_info = self->mod_info;
+
+	/* Initialize shared members */
+	pthread_mutexattr_init(&mutex_attr);
+	pthread_mutexattr_setpshared(&mutex_attr, PTHREAD_PROCESS_SHARED);
+	ASSERT_EQ(pthread_mutex_init(&mod_info->sync_lock, &mutex_attr), 0);
+	pthread_condattr_init(&cond_attr);
+	pthread_condattr_setpshared(&cond_attr, PTHREAD_PROCESS_SHARED);
+	ASSERT_EQ(pthread_cond_init(&mod_info->sync_cond, &cond_attr), 0);
+	mod_info->vma_count = self->vma_count;
+	mod_info->curr_state = INIT;
+	mod_info->exit = false;
+
+	self->pid = fork();
+	if (!self->pid) {
+		/* Child process modifying the address space */
+		int prot = PROT_READ | PROT_WRITE;
+		int i;
+
+		for (i = 0; i < mod_info->vma_count; i++) {
+			mod_info->child_mapped_addr[i] = mmap(NULL, self->page_size * 3, prot,
+					MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+			ASSERT_NE(mod_info->child_mapped_addr[i], MAP_FAILED);
+			/* change protection in adjacent maps to prevent merging */
+			prot ^= PROT_WRITE;
+		}
+		signal_state(mod_info, CHILD_READY);
+		wait_for_state(mod_info, PARENT_READY);
+		while (true) {
+			signal_state(mod_info, SETUP_READY);
+			wait_for_state(mod_info, SETUP_MODIFY_MAPS);
+			if (mod_info->exit)
+				break;
+
+			ASSERT_TRUE(mod_info->vma_modify(self));
+			signal_state(mod_info, SETUP_MAPS_MODIFIED);
+			wait_for_state(mod_info, SETUP_RESTORE_MAPS);
+			ASSERT_TRUE(mod_info->vma_restore(self));
+			signal_state(mod_info, SETUP_MAPS_RESTORED);
+
+			wait_for_state(mod_info, TEST_READY);
+			while (mod_info->curr_state != TEST_DONE) {
+				ASSERT_TRUE(mod_info->vma_modify(self));
+				ASSERT_TRUE(mod_info->vma_restore(self));
+			}
+		}
+		for (i = 0; i < mod_info->vma_count; i++)
+			munmap(mod_info->child_mapped_addr[i], self->page_size * 3);
+
+		exit(0);
+	}
+
+	switch (self->maps_file) {
+	case MAPS:
+		sprintf(fname, "/proc/%d/maps", self->pid);
+		break;
+	case SMAPS:
+		sprintf(fname, "/proc/%d/smaps", self->pid);
+		break;
+	default:
+		ksft_exit_fail();
+	}
+	self->maps_fd = open(fname, O_RDONLY);
+	ASSERT_NE(self->maps_fd, -1);
+
+	/* Wait for the child to map the VMAs */
+	wait_for_state(mod_info, CHILD_READY);
+
+	/* Read first two pages */
+	self->page1.data = malloc(self->page_size);
+	ASSERT_NE(self->page1.data, NULL);
+	self->page2.data = malloc(self->page_size);
+	ASSERT_NE(self->page2.data, NULL);
+
+	first_map_addr = (unsigned long)mod_info->child_mapped_addr[0];
+	last_map_addr = (unsigned long)mod_info->child_mapped_addr[mod_info->vma_count - 1];
+
+	self->skip_pages = locate_containing_page(self,
+					min(first_map_addr, last_map_addr),
+					self->page_size * 3);
+	ASSERT_NE(self->skip_pages, -1);
+	ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line));
+
+	/*
+	 * Find the addresses corresponding to the last line in the first page
+	 * and the first line in the last page.
+	 */
+	mod_info->addr = NULL;
+	mod_info->next_addr = NULL;
+	for (int i = 0; i < mod_info->vma_count; i++) {
+		if (mod_info->child_mapped_addr[i] == (void *)self->last_line.start_addr) {
+			mod_info->addr = mod_info->child_mapped_addr[i];
+			mod_info->prot = PROT_READ;
+			/* Even VMAs have write permission */
+			if ((i % 2) == 0)
+				mod_info->prot |= PROT_WRITE;
+		} else if (mod_info->child_mapped_addr[i] == (void *)self->first_line.start_addr) {
+			mod_info->next_addr = mod_info->child_mapped_addr[i];
+		}
+
+		if (mod_info->addr && mod_info->next_addr)
+			break;
+	}
+	ASSERT_TRUE(mod_info->addr && mod_info->next_addr);
+
+	signal_state(mod_info, PARENT_READY);
+}
+
+FIXTURE_TEARDOWN(proc_maps_race)
+{
+	int status;
+
+	stop_vma_modifier(self->mod_info);
+
+	free(self->page2.data);
+	free(self->page1.data);
+
+	for (int i = 0; i < self->vma_count; i++)
+		munmap(self->mod_info->child_mapped_addr[i], self->page_size);
+	close(self->maps_fd);
+	waitpid(self->pid, &status, 0);
+	munmap(self->mod_info, self->shared_mem_size);
+}
+
+TEST_F(proc_maps_race, test_maps_tearing_from_split)
+{
+	struct vma_modifier_info *mod_info = self->mod_info;
+
+	struct line_content split_last_line;
+	struct line_content split_first_line;
+	struct line_content restored_last_line;
+	struct line_content restored_first_line;
+
+	wait_for_state(mod_info, SETUP_READY);
+
+	/* re-read the file to avoid using stale data from previous test */
+	ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line));
+
+	mod_info->vma_modify = split_vma;
+	mod_info->vma_restore = merge_vma;
+	mod_info->vma_mod_check = check_split_result;
+
+	report_test_start("Tearing from split", self->verbose);
+	ASSERT_TRUE(capture_mod_pattern(self, &split_last_line, &split_first_line,
+					&restored_last_line, &restored_first_line));
+
+	/* Now start concurrent modifications for self->duration_sec */
+	signal_state(mod_info, TEST_READY);
+
+	struct line_content new_last_line;
+	struct line_content new_first_line;
+	struct timespec start_ts, end_ts;
+
+	clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
+	start_test_loop(&start_ts, self->verbose);
+	do {
+		bool last_line_changed;
+		bool first_line_changed;
+		unsigned long vma_start;
+		unsigned long vma_end;
+
+		ASSERT_TRUE(read_boundary_lines(self, &new_last_line, &new_first_line));
+
+		/* Check if we read vmas after split */
+		if (!strcmp(new_last_line.text, split_last_line.text)) {
+			/*
+			 * The vmas should be consistent with split results,
+			 * however if vma was concurrently restored after a
+			 * split, it can be reported twice (first the original
+			 * split one, then the same vma but extended after the
+			 * merge) because we found it as the next vma again.
+			 * In that case new first line will be the same as the
+			 * last restored line.
+			 */
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_first_line.text, split_first_line.text) &&
+					strcmp(new_first_line.text, restored_last_line.text),
+					"Split result invalid", self));
+		} else {
+			/* The vmas should be consistent with merge results */
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_last_line.text, restored_last_line.text),
+					"Merge result invalid", self));
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_first_line.text, restored_first_line.text),
+					"Merge result invalid", self));
+		}
+		/*
+		 * First and last lines should change in unison. If the last
+		 * line changed then the first line should change as well and
+		 * vice versa.
+		 */
+		last_line_changed = strcmp(new_last_line.text, self->last_line.text) != 0;
+		first_line_changed = strcmp(new_first_line.text, self->first_line.text) != 0;
+		ASSERT_EQ(last_line_changed, first_line_changed);
+		if (self->maps_file == MAPS) {
+			/* Check if PROCMAP_QUERY ioclt() finds the right VMA */
+			ASSERT_TRUE(query_addr_at(self->maps_fd, mod_info->addr + self->page_size,
+						  &vma_start, &vma_end));
+			/*
+			 * The vma at the split address can be either the same as
+			 * original one (if read before the split) or the same as the
+			 * first line in the second page (if read after the split).
+			 */
+			ASSERT_TRUE((vma_start == self->last_line.start_addr &&
+				     vma_end == self->last_line.end_addr) ||
+				    (vma_start == split_first_line.start_addr &&
+				     vma_end == split_first_line.end_addr));
+		}
+		clock_gettime(CLOCK_MONOTONIC_COARSE, &end_ts);
+		end_test_iteration(&end_ts, self->verbose);
+	} while (end_ts.tv_sec - start_ts.tv_sec < self->duration_sec);
+	end_test_loop(self->verbose);
+
+	/* Signal the modifyer thread to stop and wait until it exits */
+	signal_state(mod_info, TEST_DONE);
+}
+
+TEST_F(proc_maps_race, test_maps_tearing_from_resize)
+{
+	struct vma_modifier_info *mod_info = self->mod_info;
+
+	struct line_content shrunk_last_line;
+	struct line_content shrunk_first_line;
+	struct line_content restored_last_line;
+	struct line_content restored_first_line;
+
+	wait_for_state(mod_info, SETUP_READY);
+
+	/* re-read the file to avoid using stale data from previous test */
+	ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line));
+
+	mod_info->vma_modify = shrink_vma;
+	mod_info->vma_restore = expand_vma;
+	mod_info->vma_mod_check = check_shrink_result;
+
+	report_test_start("Tearing from resize", self->verbose);
+	ASSERT_TRUE(capture_mod_pattern(self, &shrunk_last_line, &shrunk_first_line,
+					&restored_last_line, &restored_first_line));
+
+	/* Now start concurrent modifications for self->duration_sec */
+	signal_state(mod_info, TEST_READY);
+
+	struct line_content new_last_line;
+	struct line_content new_first_line;
+	struct timespec start_ts, end_ts;
+
+	clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
+	start_test_loop(&start_ts, self->verbose);
+	do {
+		unsigned long vma_start;
+		unsigned long vma_end;
+
+		ASSERT_TRUE(read_boundary_lines(self, &new_last_line, &new_first_line));
+
+		/* Check if we read vmas after shrinking it */
+		if (!strcmp(new_last_line.text, shrunk_last_line.text)) {
+			/*
+			 * The vmas should be consistent with shrunk results,
+			 * however if the vma was concurrently restored, it
+			 * can be reported twice (first as shrunk one, then
+			 * as restored one) because we found it as the next vma
+			 * again. In that case new first line will be the same
+			 * as the last restored line.
+			 */
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_first_line.text, shrunk_first_line.text) &&
+					strcmp(new_first_line.text, restored_last_line.text),
+					"Shrink result invalid", self));
+		} else {
+			/* The vmas should be consistent with the original/resored state */
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_last_line.text, restored_last_line.text),
+					"Expand result invalid", self));
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_first_line.text, restored_first_line.text),
+					"Expand result invalid", self));
+		}
+		if (self->maps_file == MAPS) {
+			/* Check if PROCMAP_QUERY ioclt() finds the right VMA */
+			ASSERT_TRUE(query_addr_at(self->maps_fd, mod_info->addr,
+						  &vma_start, &vma_end));
+			/*
+			 * The vma should stay at the same address and have either the
+			 * original size of 3 pages or 1 page if read after shrinking.
+			 */
+			ASSERT_TRUE(vma_start == self->last_line.start_addr &&
+				    (vma_end - vma_start == self->page_size * 3 ||
+				     vma_end - vma_start == self->page_size));
+		}
+		clock_gettime(CLOCK_MONOTONIC_COARSE, &end_ts);
+		end_test_iteration(&end_ts, self->verbose);
+	} while (end_ts.tv_sec - start_ts.tv_sec < self->duration_sec);
+	end_test_loop(self->verbose);
+
+	/* Signal the modifyer thread to stop and wait until it exits */
+	signal_state(mod_info, TEST_DONE);
+}
+
+TEST_F(proc_maps_race, test_maps_tearing_from_remap)
+{
+	struct vma_modifier_info *mod_info = self->mod_info;
+
+	struct line_content remapped_last_line;
+	struct line_content remapped_first_line;
+	struct line_content restored_last_line;
+	struct line_content restored_first_line;
+
+	wait_for_state(mod_info, SETUP_READY);
+
+	/* re-read the file to avoid using stale data from previous test */
+	ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line));
+
+	mod_info->vma_modify = remap_vma;
+	mod_info->vma_restore = patch_vma;
+	mod_info->vma_mod_check = check_remap_result;
+
+	report_test_start("Tearing from remap", self->verbose);
+	ASSERT_TRUE(capture_mod_pattern(self, &remapped_last_line, &remapped_first_line,
+					&restored_last_line, &restored_first_line));
+
+	/* Now start concurrent modifications for self->duration_sec */
+	signal_state(mod_info, TEST_READY);
+
+	struct line_content new_last_line;
+	struct line_content new_first_line;
+	struct timespec start_ts, end_ts;
+
+	clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
+	start_test_loop(&start_ts, self->verbose);
+	do {
+		unsigned long vma_start;
+		unsigned long vma_end;
+
+		ASSERT_TRUE(read_boundary_lines(self, &new_last_line, &new_first_line));
+
+		/* Check if we read vmas after remapping it */
+		if (!strcmp(new_last_line.text, remapped_last_line.text)) {
+			/*
+			 * The vmas should be consistent with remap results,
+			 * however if the vma was concurrently restored, it
+			 * can be reported twice (first as split one, then
+			 * as restored one) because we found it as the next vma
+			 * again. In that case new first line will be the same
+			 * as the last restored line.
+			 */
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_first_line.text, remapped_first_line.text) &&
+					strcmp(new_first_line.text, restored_last_line.text),
+					"Remap result invalid", self));
+		} else {
+			/* The vmas should be consistent with the original/resored state */
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_last_line.text, restored_last_line.text),
+					"Remap restore result invalid", self));
+			ASSERT_FALSE(print_boundaries_on(
+					strcmp(new_first_line.text, restored_first_line.text),
+					"Remap restore result invalid", self));
+		}
+		if (self->maps_file == MAPS) {
+			/* Check if PROCMAP_QUERY ioclt() finds the right VMA */
+			ASSERT_TRUE(query_addr_at(self->maps_fd, mod_info->addr + self->page_size,
+						  &vma_start, &vma_end));
+			/*
+			 * The vma should either stay at the same address and have the
+			 * original size of 3 pages or we should find the remapped vma
+			 * at the remap destination address with size of 1 page.
+			 */
+			ASSERT_TRUE((vma_start == self->last_line.start_addr &&
+				     vma_end - vma_start == self->page_size * 3) ||
+				    (vma_start == self->last_line.start_addr + self->page_size &&
+				     vma_end - vma_start == self->page_size));
+		}
+		clock_gettime(CLOCK_MONOTONIC_COARSE, &end_ts);
+		end_test_iteration(&end_ts, self->verbose);
+	} while (end_ts.tv_sec - start_ts.tv_sec < self->duration_sec);
+	end_test_loop(self->verbose);
+
+	/* Signal the modifyer thread to stop and wait until it exits */
+	signal_state(mod_info, TEST_DONE);
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/proc/proc-multiple-procfs.c b/tools/testing/selftests/proc/proc-multiple-procfs.c
new file mode 100644
index 000000000..ab912ad95
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-multiple-procfs.c
@@ -0,0 +1,48 @@
+/*
+ * Copyright © 2020 Alexey Gladkov <gladkov.alexey@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+int main(void)
+{
+	struct stat proc_st1, proc_st2;
+	char procbuff[] = "/tmp/proc.XXXXXX/meminfo";
+	char procdir1[] = "/tmp/proc.XXXXXX";
+	char procdir2[] = "/tmp/proc.XXXXXX";
+
+	assert(mkdtemp(procdir1) != NULL);
+	assert(mkdtemp(procdir2) != NULL);
+
+	assert(!mount("proc", procdir1, "proc", 0, "hidepid=1"));
+	assert(!mount("proc", procdir2, "proc", 0, "hidepid=2"));
+
+	snprintf(procbuff, sizeof(procbuff), "%s/meminfo", procdir1);
+	assert(!stat(procbuff, &proc_st1));
+
+	snprintf(procbuff, sizeof(procbuff), "%s/meminfo", procdir2);
+	assert(!stat(procbuff, &proc_st2));
+
+	umount(procdir1);
+	umount(procdir2);
+
+	assert(proc_st1.st_dev != proc_st2.st_dev);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-net-dev-lseek.c b/tools/testing/selftests/proc/proc-net-dev-lseek.c
new file mode 100644
index 000000000..742a3e804
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-net-dev-lseek.c
@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2025 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#undef _GNU_SOURCE
+#define _GNU_SOURCE
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <sched.h>
+/*
+ * Test that lseek("/proc/net/dev/", 0, SEEK_SET)
+ * a) works,
+ * b) does what you think it does.
+ */
+int main(void)
+{
+	/* /proc/net/dev output is deterministic in fresh netns only. */
+	if (unshare(CLONE_NEWNET) == -1) {
+		if (errno == ENOSYS || errno == EPERM) {
+			return 4;
+		}
+		return 1;
+	}
+
+	const int fd = open("/proc/net/dev", O_RDONLY);
+	assert(fd >= 0);
+
+	char buf1[4096];
+	const ssize_t rv1 = read(fd, buf1, sizeof(buf1));
+	/*
+	 * Not "<=", this file can't be empty:
+	 * there is header, "lo" interface with some zeroes.
+	 */
+	assert(0 < rv1);
+	assert(rv1 <= sizeof(buf1));
+
+	/* Believe it or not, this line broke one day. */
+	assert(lseek(fd, 0, SEEK_SET) == 0);
+
+	char buf2[4096];
+	const ssize_t rv2 = read(fd, buf2, sizeof(buf2));
+	/* Not "<=", see above. */
+	assert(0 < rv2);
+	assert(rv2 <= sizeof(buf2));
+
+	/* Test that lseek rewinds to the beginning of the file. */
+	assert(rv1 == rv2);
+	assert(memcmp(buf1, buf2, rv1) == 0);
+
+	/* Contents of the file is not validated: this test is about lseek(). */
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-pid-vm.c b/tools/testing/selftests/proc/proc-pid-vm.c
new file mode 100644
index 000000000..4e6a3e53f
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-pid-vm.c
@@ -0,0 +1,592 @@
+/*
+ * Copyright (c) 2019 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * Fork and exec tiny 1 page executable which precisely controls its VM.
+ * Test /proc/$PID/maps
+ * Test /proc/$PID/smaps
+ * Test /proc/$PID/smaps_rollup
+ * Test /proc/$PID/statm
+ *
+ * FIXME require CONFIG_TMPFS which can be disabled
+ * FIXME test other values from "smaps"
+ * FIXME support other archs
+ */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <sys/uio.h>
+#include <linux/kdev_t.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <linux/fs.h>
+
+#ifndef __maybe_unused
+#define __maybe_unused __attribute__((__unused__))
+#endif
+
+#include "kselftest.h"
+
+static inline long sys_execveat(int dirfd, const char *pathname, char **argv, char **envp, int flags)
+{
+	return syscall(SYS_execveat, dirfd, pathname, argv, envp, flags);
+}
+
+static void make_private_tmp(void)
+{
+	if (unshare(CLONE_NEWNS) == -1) {
+		if (errno == ENOSYS || errno == EPERM) {
+			exit(4);
+		}
+		exit(1);
+	}
+	if (mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL) == -1) {
+		exit(1);
+	}
+	if (mount(NULL, "/tmp", "tmpfs", 0, NULL) == -1) {
+		exit(1);
+	}
+}
+
+static pid_t pid = -1;
+static void ate(void)
+{
+	if (pid > 0) {
+		kill(pid, SIGTERM);
+	}
+}
+
+struct elf64_hdr {
+	uint8_t e_ident[16];
+	uint16_t e_type;
+	uint16_t e_machine;
+	uint32_t e_version;
+	uint64_t e_entry;
+	uint64_t e_phoff;
+	uint64_t e_shoff;
+	uint32_t e_flags;
+	uint16_t e_ehsize;
+	uint16_t e_phentsize;
+	uint16_t e_phnum;
+	uint16_t e_shentsize;
+	uint16_t e_shnum;
+	uint16_t e_shstrndx;
+};
+
+struct elf64_phdr {
+	uint32_t p_type;
+	uint32_t p_flags;
+	uint64_t p_offset;
+	uint64_t p_vaddr;
+	uint64_t p_paddr;
+	uint64_t p_filesz;
+	uint64_t p_memsz;
+	uint64_t p_align;
+};
+
+#ifdef __x86_64__
+#define PAGE_SIZE 4096
+#define VADDR (1UL << 32)
+#define MAPS_OFFSET 73
+
+#define syscall	0x0f, 0x05
+#define mov_rdi(x)	\
+	0x48, 0xbf,	\
+	(x)&0xff, ((x)>>8)&0xff, ((x)>>16)&0xff, ((x)>>24)&0xff,	\
+	((x)>>32)&0xff, ((x)>>40)&0xff, ((x)>>48)&0xff, ((x)>>56)&0xff
+
+#define mov_rsi(x)	\
+	0x48, 0xbe,	\
+	(x)&0xff, ((x)>>8)&0xff, ((x)>>16)&0xff, ((x)>>24)&0xff,	\
+	((x)>>32)&0xff, ((x)>>40)&0xff, ((x)>>48)&0xff, ((x)>>56)&0xff
+
+#define mov_eax(x)	\
+	0xb8, (x)&0xff, ((x)>>8)&0xff, ((x)>>16)&0xff, ((x)>>24)&0xff
+
+static const uint8_t payload[] = {
+	/* Casually unmap stack, vDSO and everything else. */
+	/* munmap */
+	mov_rdi(VADDR + 4096),
+	mov_rsi((1ULL << 47) - 4096 - VADDR - 4096),
+	mov_eax(11),
+	syscall,
+
+	/* Ping parent. */
+	/* write(0, &c, 1); */
+	0x31, 0xff,					/* xor edi, edi */
+	0x48, 0x8d, 0x35, 0x00, 0x00, 0x00, 0x00,	/* lea rsi, [rip] */
+	0xba, 0x01, 0x00, 0x00, 0x00,			/* mov edx, 1 */
+	mov_eax(1),
+	syscall,
+
+	/* 1: pause(); */
+	mov_eax(34),
+	syscall,
+
+	0xeb, 0xf7,	/* jmp 1b */
+};
+
+static int make_exe(const uint8_t *payload, size_t len)
+{
+	struct elf64_hdr h;
+	struct elf64_phdr ph;
+
+	struct iovec iov[3] = {
+		{&h, sizeof(struct elf64_hdr)},
+		{&ph, sizeof(struct elf64_phdr)},
+		{(void *)payload, len},
+	};
+	int fd, fd1;
+	char buf[64];
+
+	memset(&h, 0, sizeof(h));
+	h.e_ident[0] = 0x7f;
+	h.e_ident[1] = 'E';
+	h.e_ident[2] = 'L';
+	h.e_ident[3] = 'F';
+	h.e_ident[4] = 2;
+	h.e_ident[5] = 1;
+	h.e_ident[6] = 1;
+	h.e_ident[7] = 0;
+	h.e_type = 2;
+	h.e_machine = 0x3e;
+	h.e_version = 1;
+	h.e_entry = VADDR + sizeof(struct elf64_hdr) + sizeof(struct elf64_phdr);
+	h.e_phoff = sizeof(struct elf64_hdr);
+	h.e_shoff = 0;
+	h.e_flags = 0;
+	h.e_ehsize = sizeof(struct elf64_hdr);
+	h.e_phentsize = sizeof(struct elf64_phdr);
+	h.e_phnum = 1;
+	h.e_shentsize = 0;
+	h.e_shnum = 0;
+	h.e_shstrndx = 0;
+
+	memset(&ph, 0, sizeof(ph));
+	ph.p_type = 1;
+	ph.p_flags = (1<<2)|1;
+	ph.p_offset = 0;
+	ph.p_vaddr = VADDR;
+	ph.p_paddr = 0;
+	ph.p_filesz = sizeof(struct elf64_hdr) + sizeof(struct elf64_phdr) + len;
+	ph.p_memsz = sizeof(struct elf64_hdr) + sizeof(struct elf64_phdr) + len;
+	ph.p_align = 4096;
+
+	fd = openat(AT_FDCWD, "/tmp", O_WRONLY|O_EXCL|O_TMPFILE, 0700);
+	if (fd == -1) {
+		exit(1);
+	}
+
+	if (writev(fd, iov, 3) != sizeof(struct elf64_hdr) + sizeof(struct elf64_phdr) + len) {
+		exit(1);
+	}
+
+	/* Avoid ETXTBSY on exec. */
+	snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd);
+	fd1 = open(buf, O_RDONLY|O_CLOEXEC);
+	close(fd);
+
+	return fd1;
+}
+#endif
+
+/*
+ * 0: vsyscall VMA doesn't exist	vsyscall=none
+ * 1: vsyscall VMA is --xp		vsyscall=xonly
+ * 2: vsyscall VMA is r-xp		vsyscall=emulate
+ */
+static volatile int g_vsyscall;
+static const char *str_vsyscall __maybe_unused;
+
+static const char str_vsyscall_0[] __maybe_unused = "";
+static const char str_vsyscall_1[] __maybe_unused =
+"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0                  [vsyscall]\n";
+static const char str_vsyscall_2[] __maybe_unused =
+"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n";
+
+#ifdef __x86_64__
+static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
+{
+	_exit(g_vsyscall);
+}
+
+/*
+ * vsyscall page can't be unmapped, probe it directly.
+ */
+static void vsyscall(void)
+{
+	pid_t pid;
+	int wstatus;
+
+	pid = fork();
+	if (pid < 0) {
+		fprintf(stderr, "fork, errno %d\n", errno);
+		exit(1);
+	}
+	if (pid == 0) {
+		struct rlimit rlim = {0, 0};
+		(void)setrlimit(RLIMIT_CORE, &rlim);
+
+		/* Hide "segfault at ffffffffff600000" messages. */
+		struct sigaction act;
+		memset(&act, 0, sizeof(struct sigaction));
+		act.sa_flags = SA_SIGINFO;
+		act.sa_sigaction = sigaction_SIGSEGV;
+		(void)sigaction(SIGSEGV, &act, NULL);
+
+		g_vsyscall = 0;
+		/* gettimeofday(NULL, NULL); */
+		uint64_t rax = 0xffffffffff600000;
+		asm volatile (
+			"call *%[rax]"
+			: [rax] "+a" (rax)
+			: "D" (NULL), "S" (NULL)
+			: "rcx", "r11"
+		);
+
+		g_vsyscall = 1;
+		*(volatile int *)0xffffffffff600000UL;
+
+		g_vsyscall = 2;
+		exit(g_vsyscall);
+	}
+	waitpid(pid, &wstatus, 0);
+	if (WIFEXITED(wstatus)) {
+		g_vsyscall = WEXITSTATUS(wstatus);
+	} else {
+		fprintf(stderr, "error: wstatus %08x\n", wstatus);
+		exit(1);
+	}
+}
+
+int main(void)
+{
+	int pipefd[2];
+	int exec_fd;
+
+	vsyscall();
+	switch (g_vsyscall) {
+	case 0:
+		str_vsyscall = str_vsyscall_0;
+		break;
+	case 1:
+		str_vsyscall = str_vsyscall_1;
+		break;
+	case 2:
+		str_vsyscall = str_vsyscall_2;
+		break;
+	default:
+		abort();
+	}
+
+	atexit(ate);
+
+	make_private_tmp();
+
+	/* Reserve fd 0 for 1-byte pipe ping from child. */
+	close(0);
+	if (open("/", O_RDONLY|O_DIRECTORY|O_PATH) != 0) {
+		return 1;
+	}
+
+	exec_fd = make_exe(payload, sizeof(payload));
+
+	if (pipe(pipefd) == -1) {
+		return 1;
+	}
+	if (dup2(pipefd[1], 0) != 0) {
+		return 1;
+	}
+
+	pid = fork();
+	if (pid == -1) {
+		return 1;
+	}
+	if (pid == 0) {
+		sys_execveat(exec_fd, "", NULL, NULL, AT_EMPTY_PATH);
+		return 1;
+	}
+
+	char _;
+	if (read(pipefd[0], &_, 1) != 1) {
+		return 1;
+	}
+
+	struct stat st;
+	if (fstat(exec_fd, &st) == -1) {
+		return 1;
+	}
+
+	/* Generate "head -n1 /proc/$PID/maps" */
+	char buf0[256];
+	memset(buf0, ' ', sizeof(buf0));
+	int len = snprintf(buf0, sizeof(buf0),
+			"%08lx-%08lx r-xp 00000000 %02lx:%02lx %llu",
+			VADDR, VADDR + PAGE_SIZE,
+			MAJOR(st.st_dev), MINOR(st.st_dev),
+			(unsigned long long)st.st_ino);
+	buf0[len] = ' ';
+	snprintf(buf0 + MAPS_OFFSET, sizeof(buf0) - MAPS_OFFSET,
+		 "/tmp/#%llu (deleted)\n", (unsigned long long)st.st_ino);
+
+	/* Test /proc/$PID/maps */
+	{
+		const size_t len = strlen(buf0) + strlen(str_vsyscall);
+		char buf[256];
+		ssize_t rv;
+		int fd;
+
+		snprintf(buf, sizeof(buf), "/proc/%u/maps", pid);
+		fd = open(buf, O_RDONLY);
+		if (fd == -1) {
+			return 1;
+		}
+		rv = read(fd, buf, sizeof(buf));
+		assert(rv == len);
+		assert(memcmp(buf, buf0, strlen(buf0)) == 0);
+		if (g_vsyscall > 0) {
+			assert(memcmp(buf + strlen(buf0), str_vsyscall, strlen(str_vsyscall)) == 0);
+		}
+	}
+
+	/* Test /proc/$PID/smaps */
+	{
+		char buf[4096];
+		ssize_t rv;
+		int fd;
+
+		snprintf(buf, sizeof(buf), "/proc/%u/smaps", pid);
+		fd = open(buf, O_RDONLY);
+		if (fd == -1) {
+			return 1;
+		}
+		rv = read(fd, buf, sizeof(buf));
+		assert(0 <= rv && rv <= sizeof(buf));
+
+		assert(rv >= strlen(buf0));
+		assert(memcmp(buf, buf0, strlen(buf0)) == 0);
+
+#define RSS1 "Rss:                   4 kB\n"
+#define RSS2 "Rss:                   0 kB\n"
+#define PSS1 "Pss:                   4 kB\n"
+#define PSS2 "Pss:                   0 kB\n"
+		assert(memmem(buf, rv, RSS1, strlen(RSS1)) ||
+		       memmem(buf, rv, RSS2, strlen(RSS2)));
+		assert(memmem(buf, rv, PSS1, strlen(PSS1)) ||
+		       memmem(buf, rv, PSS2, strlen(PSS2)));
+
+		static const char *S[] = {
+			"Size:                  4 kB\n",
+			"KernelPageSize:        4 kB\n",
+			"MMUPageSize:           4 kB\n",
+			"Anonymous:             0 kB\n",
+			"AnonHugePages:         0 kB\n",
+			"Shared_Hugetlb:        0 kB\n",
+			"Private_Hugetlb:       0 kB\n",
+			"Locked:                0 kB\n",
+		};
+		int i;
+
+		for (i = 0; i < ARRAY_SIZE(S); i++) {
+			assert(memmem(buf, rv, S[i], strlen(S[i])));
+		}
+
+		if (g_vsyscall > 0) {
+			assert(memmem(buf, rv, str_vsyscall, strlen(str_vsyscall)));
+		}
+	}
+
+	/* Test /proc/$PID/smaps_rollup */
+	{
+		char bufr[256];
+		memset(bufr, ' ', sizeof(bufr));
+		len = snprintf(bufr, sizeof(bufr),
+				"%08lx-%08lx ---p 00000000 00:00 0",
+				VADDR, VADDR + PAGE_SIZE);
+		bufr[len] = ' ';
+		snprintf(bufr + MAPS_OFFSET, sizeof(bufr) - MAPS_OFFSET,
+			 "[rollup]\n");
+
+		char buf[1024];
+		ssize_t rv;
+		int fd;
+
+		snprintf(buf, sizeof(buf), "/proc/%u/smaps_rollup", pid);
+		fd = open(buf, O_RDONLY);
+		if (fd == -1) {
+			return 1;
+		}
+		rv = read(fd, buf, sizeof(buf));
+		assert(0 <= rv && rv <= sizeof(buf));
+
+		assert(rv >= strlen(bufr));
+		assert(memcmp(buf, bufr, strlen(bufr)) == 0);
+
+		assert(memmem(buf, rv, RSS1, strlen(RSS1)) ||
+		       memmem(buf, rv, RSS2, strlen(RSS2)));
+		assert(memmem(buf, rv, PSS1, strlen(PSS1)) ||
+		       memmem(buf, rv, PSS2, strlen(PSS2)));
+
+		static const char *S[] = {
+			"Anonymous:             0 kB\n",
+			"AnonHugePages:         0 kB\n",
+			"Shared_Hugetlb:        0 kB\n",
+			"Private_Hugetlb:       0 kB\n",
+			"Locked:                0 kB\n",
+		};
+		int i;
+
+		for (i = 0; i < ARRAY_SIZE(S); i++) {
+			assert(memmem(buf, rv, S[i], strlen(S[i])));
+		}
+	}
+
+	/* Test /proc/$PID/statm */
+	{
+		char buf[64];
+		ssize_t rv;
+		int fd;
+
+		snprintf(buf, sizeof(buf), "/proc/%u/statm", pid);
+		fd = open(buf, O_RDONLY);
+		if (fd == -1) {
+			return 1;
+		}
+		rv = read(fd, buf, sizeof(buf));
+		assert(rv == 7 * 2);
+
+		assert(buf[0] == '1');	/* ->total_vm */
+		assert(buf[1] == ' ');
+		assert(buf[2] == '0' || buf[2] == '1');	/* rss */
+		assert(buf[3] == ' ');
+		assert(buf[4] == '0' || buf[2] == '1');	/* file rss */
+		assert(buf[5] == ' ');
+		assert(buf[6] == '1');	/* ELF executable segments */
+		assert(buf[7] == ' ');
+		assert(buf[8] == '0');
+		assert(buf[9] == ' ');
+		assert(buf[10] == '0');	/* ->data_vm + ->stack_vm */
+		assert(buf[11] == ' ');
+		assert(buf[12] == '0');
+		assert(buf[13] == '\n');
+	}
+
+	/* Test PROCMAP_QUERY ioctl() for /proc/$PID/maps */
+	{
+		char path_buf[256], exp_path_buf[256];
+		struct procmap_query q;
+		int fd, err;
+
+		snprintf(path_buf, sizeof(path_buf), "/proc/%u/maps", pid);
+		fd = open(path_buf, O_RDONLY);
+		if (fd == -1)
+			return 1;
+
+		/* CASE 1: exact MATCH at VADDR */
+		memset(&q, 0, sizeof(q));
+		q.size = sizeof(q);
+		q.query_addr = VADDR;
+		q.query_flags = 0;
+		q.vma_name_addr = (__u64)(unsigned long)path_buf;
+		q.vma_name_size = sizeof(path_buf);
+
+		err = ioctl(fd, PROCMAP_QUERY, &q);
+		assert(err == 0);
+
+		assert(q.query_addr == VADDR);
+		assert(q.query_flags == 0);
+
+		assert(q.vma_flags == (PROCMAP_QUERY_VMA_READABLE | PROCMAP_QUERY_VMA_EXECUTABLE));
+		assert(q.vma_start == VADDR);
+		assert(q.vma_end == VADDR + PAGE_SIZE);
+		assert(q.vma_page_size == PAGE_SIZE);
+
+		assert(q.vma_offset == 0);
+		assert(q.inode == st.st_ino);
+		assert(q.dev_major == MAJOR(st.st_dev));
+		assert(q.dev_minor == MINOR(st.st_dev));
+
+		snprintf(exp_path_buf, sizeof(exp_path_buf),
+			"/tmp/#%llu (deleted)", (unsigned long long)st.st_ino);
+		assert(q.vma_name_size == strlen(exp_path_buf) + 1);
+		assert(strcmp(path_buf, exp_path_buf) == 0);
+
+		/* CASE 2: NO MATCH at VADDR-1 */
+		memset(&q, 0, sizeof(q));
+		q.size = sizeof(q);
+		q.query_addr = VADDR - 1;
+		q.query_flags = 0; /* exact match */
+
+		err = ioctl(fd, PROCMAP_QUERY, &q);
+		err = err < 0 ? -errno : 0;
+		assert(err == -ENOENT);
+
+		/* CASE 3: MATCH COVERING_OR_NEXT_VMA at VADDR - 1 */
+		memset(&q, 0, sizeof(q));
+		q.size = sizeof(q);
+		q.query_addr = VADDR - 1;
+		q.query_flags = PROCMAP_QUERY_COVERING_OR_NEXT_VMA;
+
+		err = ioctl(fd, PROCMAP_QUERY, &q);
+		assert(err == 0);
+
+		assert(q.query_addr == VADDR - 1);
+		assert(q.query_flags == PROCMAP_QUERY_COVERING_OR_NEXT_VMA);
+		assert(q.vma_start == VADDR);
+		assert(q.vma_end == VADDR + PAGE_SIZE);
+
+		/* CASE 4: NO MATCH at VADDR + PAGE_SIZE */
+		memset(&q, 0, sizeof(q));
+		q.size = sizeof(q);
+		q.query_addr = VADDR + PAGE_SIZE; /* point right after the VMA */
+		q.query_flags = PROCMAP_QUERY_COVERING_OR_NEXT_VMA;
+
+		err = ioctl(fd, PROCMAP_QUERY, &q);
+		err = err < 0 ? -errno : 0;
+		assert(err == -ENOENT);
+
+		/* CASE 5: NO MATCH WRITABLE at VADDR */
+		memset(&q, 0, sizeof(q));
+		q.size = sizeof(q);
+		q.query_addr = VADDR;
+		q.query_flags = PROCMAP_QUERY_VMA_WRITABLE;
+
+		err = ioctl(fd, PROCMAP_QUERY, &q);
+		err = err < 0 ? -errno : 0;
+		assert(err == -ENOENT);
+	}
+
+	return 0;
+}
+#else
+int main(void)
+{
+	return 4;
+}
+#endif
diff --git a/tools/testing/selftests/proc/proc-pidns.c b/tools/testing/selftests/proc/proc-pidns.c
new file mode 100644
index 000000000..6f7c10fe9
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-pidns.c
@@ -0,0 +1,212 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Author: Aleksa Sarai <cyphar@cyphar.com>
+ * Copyright (C) 2025 SUSE LLC.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/prctl.h>
+
+#include "kselftest_harness.h"
+
+#define ASSERT_ERRNO(expected, _t, seen)				\
+	__EXPECT(expected, #expected,					\
+		({__typeof__(seen) _tmp_seen = (seen);			\
+		  _tmp_seen >= 0 ? _tmp_seen : -errno; }), #seen, _t, 1)
+
+#define ASSERT_ERRNO_EQ(expected, seen) \
+	ASSERT_ERRNO(expected, ==, seen)
+
+#define ASSERT_SUCCESS(seen) \
+	ASSERT_ERRNO(0, <=, seen)
+
+static int touch(char *path)
+{
+	int fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC, 0644);
+	if (fd < 0)
+		return -1;
+	return close(fd);
+}
+
+FIXTURE(ns)
+{
+	int host_mntns, host_pidns;
+	int dummy_pidns;
+};
+
+FIXTURE_SETUP(ns)
+{
+	/* Stash the old mntns. */
+	self->host_mntns = open("/proc/self/ns/mnt", O_RDONLY|O_CLOEXEC);
+	ASSERT_SUCCESS(self->host_mntns);
+
+	/* Create a new mount namespace and make it private. */
+	ASSERT_SUCCESS(unshare(CLONE_NEWNS));
+	ASSERT_SUCCESS(mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL));
+
+	/*
+	 * Create a proper tmpfs that we can use and will disappear once we
+	 * leave this mntns.
+	 */
+	ASSERT_SUCCESS(mount("tmpfs", "/tmp", "tmpfs", 0, NULL));
+
+	/*
+	 * Create a pidns we can use for later tests. We need to fork off a
+	 * child so that we get a usable nsfd that we can bind-mount and open.
+	 */
+	ASSERT_SUCCESS(mkdir("/tmp/dummy", 0755));
+	ASSERT_SUCCESS(touch("/tmp/dummy/pidns"));
+	ASSERT_SUCCESS(mkdir("/tmp/dummy/proc", 0755));
+
+	self->host_pidns = open("/proc/self/ns/pid", O_RDONLY|O_CLOEXEC);
+	ASSERT_SUCCESS(self->host_pidns);
+	ASSERT_SUCCESS(unshare(CLONE_NEWPID));
+
+	pid_t pid = fork();
+	ASSERT_SUCCESS(pid);
+	if (!pid) {
+		prctl(PR_SET_PDEATHSIG, SIGKILL);
+		ASSERT_SUCCESS(mount("/proc/self/ns/pid", "/tmp/dummy/pidns", NULL, MS_BIND, NULL));
+		ASSERT_SUCCESS(mount("proc", "/tmp/dummy/proc", "proc", 0, NULL));
+		exit(0);
+	}
+
+	int wstatus;
+	ASSERT_EQ(waitpid(pid, &wstatus, 0), pid);
+	ASSERT_TRUE(WIFEXITED(wstatus));
+	ASSERT_EQ(WEXITSTATUS(wstatus), 0);
+
+	ASSERT_SUCCESS(setns(self->host_pidns, CLONE_NEWPID));
+
+	self->dummy_pidns = open("/tmp/dummy/pidns", O_RDONLY|O_CLOEXEC);
+	ASSERT_SUCCESS(self->dummy_pidns);
+}
+
+FIXTURE_TEARDOWN(ns)
+{
+	ASSERT_SUCCESS(setns(self->host_mntns, CLONE_NEWNS));
+	ASSERT_SUCCESS(close(self->host_mntns));
+
+	ASSERT_SUCCESS(close(self->host_pidns));
+	ASSERT_SUCCESS(close(self->dummy_pidns));
+}
+
+TEST_F(ns, pidns_mount_string_path)
+{
+	ASSERT_SUCCESS(mkdir("/tmp/proc-host", 0755));
+	ASSERT_SUCCESS(mount("proc", "/tmp/proc-host", "proc", 0, "pidns=/proc/self/ns/pid"));
+	ASSERT_SUCCESS(access("/tmp/proc-host/self/", X_OK));
+
+	ASSERT_SUCCESS(mkdir("/tmp/proc-dummy", 0755));
+	ASSERT_SUCCESS(mount("proc", "/tmp/proc-dummy", "proc", 0, "pidns=/tmp/dummy/pidns"));
+	ASSERT_ERRNO_EQ(-ENOENT, access("/tmp/proc-dummy/1/", X_OK));
+	ASSERT_ERRNO_EQ(-ENOENT, access("/tmp/proc-dummy/self/", X_OK));
+}
+
+TEST_F(ns, pidns_fsconfig_string_path)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_SUCCESS(fsfd);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_STRING, "pidns", "/tmp/dummy/pidns", 0));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_SUCCESS(mountfd);
+
+	ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+TEST_F(ns, pidns_fsconfig_fd)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_SUCCESS(fsfd);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_SUCCESS(mountfd);
+
+	ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_ERRNO_EQ(-ENOENT, faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+TEST_F(ns, pidns_reconfigure_remount)
+{
+	ASSERT_SUCCESS(mkdir("/tmp/proc", 0755));
+	ASSERT_SUCCESS(mount("proc", "/tmp/proc", "proc", 0, ""));
+
+	ASSERT_SUCCESS(access("/tmp/proc/1/", X_OK));
+	ASSERT_SUCCESS(access("/tmp/proc/self/", X_OK));
+
+	ASSERT_ERRNO_EQ(-EBUSY, mount(NULL, "/tmp/proc", NULL, MS_REMOUNT, "pidns=/tmp/dummy/pidns"));
+
+	ASSERT_SUCCESS(access("/tmp/proc/1/", X_OK));
+	ASSERT_SUCCESS(access("/tmp/proc/self/", X_OK));
+}
+
+TEST_F(ns, pidns_reconfigure_fsconfig_string_path)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_SUCCESS(fsfd);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_SUCCESS(mountfd);
+
+	ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_ERRNO_EQ(-EBUSY, fsconfig(fsfd, FSCONFIG_SET_STRING, "pidns", "/tmp/dummy/pidns", 0));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0)); /* noop */
+
+	ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+TEST_F(ns, pidns_reconfigure_fsconfig_fd)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_SUCCESS(fsfd);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_SUCCESS(mountfd);
+
+	ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_ERRNO_EQ(-EBUSY, fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0)); /* noop */
+
+	ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/proc/proc-self-isnt-kthread.c b/tools/testing/selftests/proc/proc-self-isnt-kthread.c
new file mode 100644
index 000000000..e01f4e0a9
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-isnt-kthread.c
@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2024 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test that userspace program is not kernel thread. */
+#undef NDEBUG
+#include <assert.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(void)
+{
+	int fd = open("/proc/self/status", O_RDONLY);
+	assert(fd >= 0);
+
+	char buf[4096];
+	ssize_t rv = read(fd, buf, sizeof(buf));
+	assert(0 <= rv && rv < sizeof(buf));
+	buf[rv] = '\0';
+
+	/* This test is very much not kernel thread. */
+	assert(strstr(buf, "Kthread:\t0\n"));
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-self-map-files-001.c b/tools/testing/selftests/proc/proc-self-map-files-001.c
new file mode 100644
index 000000000..4209c6428
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-map-files-001.c
@@ -0,0 +1,82 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test readlink /proc/self/map_files/... */
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <stdlib.h>
+
+static void pass(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1)
+		exit(1);
+}
+
+static void fail(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1 && errno == ENOENT)
+		return;
+	exit(1);
+}
+
+int main(void)
+{
+	const unsigned int PAGE_SIZE = sysconf(_SC_PAGESIZE);
+	void *p;
+	int fd;
+	unsigned long a, b;
+
+	fd = open("/dev/zero", O_RDONLY);
+	if (fd == -1)
+		return 1;
+
+	p = mmap(NULL, PAGE_SIZE, PROT_NONE, MAP_PRIVATE|MAP_FILE, fd, 0);
+	if (p == MAP_FAILED)
+		return 1;
+
+	a = (unsigned long)p;
+	b = (unsigned long)p + PAGE_SIZE;
+
+	pass("/proc/self/map_files/%lx-%lx", a, b);
+	fail("/proc/self/map_files/ %lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx -%lx", a, b);
+	fail("/proc/self/map_files/%lx- %lx", a, b);
+	fail("/proc/self/map_files/%lx-%lx ", a, b);
+	fail("/proc/self/map_files/0%lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx-0%lx", a, b);
+	if (sizeof(long) == 4) {
+		fail("/proc/self/map_files/100000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-100000000%lx", a, b);
+	} else if (sizeof(long) == 8) {
+		fail("/proc/self/map_files/10000000000000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-10000000000000000%lx", a, b);
+	} else
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-self-map-files-002.c b/tools/testing/selftests/proc/proc-self-map-files-002.c
new file mode 100644
index 000000000..e6aa00a18
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-map-files-002.c
@@ -0,0 +1,94 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test readlink /proc/self/map_files/... with minimum address. */
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <stdlib.h>
+
+static void pass(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1)
+		exit(1);
+}
+
+static void fail(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1 && errno == ENOENT)
+		return;
+	exit(1);
+}
+
+int main(void)
+{
+	const int PAGE_SIZE = sysconf(_SC_PAGESIZE);
+	/*
+	 * va_max must be enough bigger than vm.mmap_min_addr, which is
+	 * 64KB/32KB by default. (depends on CONFIG_LSM_MMAP_MIN_ADDR)
+	 */
+	const unsigned long va_max = 1UL << 20;
+	unsigned long va;
+	void *p;
+	int fd;
+	unsigned long a, b;
+
+	fd = open("/dev/zero", O_RDONLY);
+	if (fd == -1)
+		return 1;
+
+	for (va = 0; va < va_max; va += PAGE_SIZE) {
+		p = mmap((void *)va, PAGE_SIZE, PROT_NONE, MAP_PRIVATE|MAP_FILE|MAP_FIXED, fd, 0);
+		if (p == (void *)va)
+			break;
+	}
+	if (va == va_max) {
+		fprintf(stderr, "error: mmap doesn't like you\n");
+		return 1;
+	}
+
+	a = (unsigned long)p;
+	b = (unsigned long)p + PAGE_SIZE;
+
+	pass("/proc/self/map_files/%lx-%lx", a, b);
+	fail("/proc/self/map_files/ %lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx -%lx", a, b);
+	fail("/proc/self/map_files/%lx- %lx", a, b);
+	fail("/proc/self/map_files/%lx-%lx ", a, b);
+	fail("/proc/self/map_files/0%lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx-0%lx", a, b);
+	if (sizeof(long) == 4) {
+		fail("/proc/self/map_files/100000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-100000000%lx", a, b);
+	} else if (sizeof(long) == 8) {
+		fail("/proc/self/map_files/10000000000000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-10000000000000000%lx", a, b);
+	} else
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-self-syscall.c b/tools/testing/selftests/proc/proc-self-syscall.c
new file mode 100644
index 000000000..8511dcfe6
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-syscall.c
@@ -0,0 +1,58 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+
+static inline ssize_t sys_read(int fd, void *buf, size_t len)
+{
+	return syscall(SYS_read, fd, buf, len);
+}
+
+int main(void)
+{
+	char buf1[64];
+	char buf2[64];
+	int fd;
+	ssize_t rv;
+
+	fd = open("/proc/self/syscall", O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT)
+			return 4;
+		return 1;
+	}
+
+	/* Do direct system call as libc can wrap anything. */
+	snprintf(buf1, sizeof(buf1), "%ld 0x%lx 0x%lx 0x%lx",
+		 (long)SYS_read, (long)fd, (long)buf2, (long)sizeof(buf2));
+
+	memset(buf2, 0, sizeof(buf2));
+	rv = sys_read(fd, buf2, sizeof(buf2));
+	if (rv < 0)
+		return 1;
+	if (rv < strlen(buf1))
+		return 1;
+	if (strncmp(buf1, buf2, strlen(buf1)) != 0)
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-self-wchan.c b/tools/testing/selftests/proc/proc-self-wchan.c
new file mode 100644
index 000000000..b467b98a4
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-wchan.c
@@ -0,0 +1,40 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <unistd.h>
+
+int main(void)
+{
+	char buf[64];
+	int fd;
+
+	fd = open("/proc/self/wchan", O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT)
+			return 4;
+		return 1;
+	}
+
+	buf[0] = '\0';
+	if (read(fd, buf, sizeof(buf)) != 1)
+		return 1;
+	if (buf[0] != '0')
+		return 1;
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-subset-pid.c b/tools/testing/selftests/proc/proc-subset-pid.c
new file mode 100644
index 000000000..d1052bcab
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-subset-pid.c
@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2021 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * Test that "mount -t proc -o subset=pid" hides everything but pids,
+ * /proc/self and /proc/thread-self.
+ */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <unistd.h>
+#include <stdio.h>
+
+static inline bool streq(const char *a, const char *b)
+{
+	return strcmp(a, b) == 0;
+}
+
+static void make_private_proc(void)
+{
+	if (unshare(CLONE_NEWNS) == -1) {
+		if (errno == ENOSYS || errno == EPERM) {
+			exit(4);
+		}
+		exit(1);
+	}
+	if (mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL) == -1) {
+		exit(1);
+	}
+	if (mount(NULL, "/proc", "proc", 0, "subset=pid") == -1) {
+		exit(1);
+	}
+}
+
+static bool string_is_pid(const char *s)
+{
+	while (1) {
+		switch (*s++) {
+		case '0':case '1':case '2':case '3':case '4':
+		case '5':case '6':case '7':case '8':case '9':
+			continue;
+
+		case '\0':
+			return true;
+
+		default:
+			return false;
+		}
+	}
+}
+
+int main(void)
+{
+	make_private_proc();
+
+	DIR *d = opendir("/proc");
+	assert(d);
+
+	struct dirent *de;
+
+	bool dot = false;
+	bool dot_dot = false;
+	bool self = false;
+	bool thread_self = false;
+
+	while ((de = readdir(d))) {
+		if (streq(de->d_name, ".")) {
+			assert(!dot);
+			dot = true;
+			assert(de->d_type == DT_DIR);
+		} else if (streq(de->d_name, "..")) {
+			assert(!dot_dot);
+			dot_dot = true;
+			assert(de->d_type == DT_DIR);
+		} else if (streq(de->d_name, "self")) {
+			assert(!self);
+			self = true;
+			assert(de->d_type == DT_LNK);
+		} else if (streq(de->d_name, "thread-self")) {
+			assert(!thread_self);
+			thread_self = true;
+			assert(de->d_type == DT_LNK);
+		} else {
+			if (!string_is_pid(de->d_name)) {
+				fprintf(stderr, "d_name '%s'\n", de->d_name);
+				assert(0);
+			}
+			assert(de->d_type == DT_DIR);
+		}
+	}
+
+	char c;
+	int rv = readlink("/proc/cpuinfo", &c, 1);
+	assert(rv == -1 && errno == ENOENT);
+
+	int fd = open("/proc/cpuinfo", O_RDONLY);
+	assert(fd == -1 && errno == ENOENT);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-tid0.c b/tools/testing/selftests/proc/proc-tid0.c
new file mode 100644
index 000000000..58c1d7c90
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-tid0.c
@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2021 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that /proc/*/task never contains "0".
+#include <sys/types.h>
+#include <dirent.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <pthread.h>
+
+static pid_t pid = -1;
+
+static void atexit_hook(void)
+{
+	if (pid > 0) {
+		kill(pid, SIGKILL);
+	}
+}
+
+static void *f(void *_)
+{
+	return NULL;
+}
+
+static void sigalrm(int _)
+{
+	exit(0);
+}
+
+int main(void)
+{
+	pid = fork();
+	if (pid == 0) {
+		/* child */
+		while (1) {
+			pthread_t pth;
+			pthread_create(&pth, NULL, f, NULL);
+			pthread_join(pth, NULL);
+		}
+	} else if (pid > 0) {
+		/* parent */
+		atexit(atexit_hook);
+
+		char buf[64];
+		snprintf(buf, sizeof(buf), "/proc/%u/task", pid);
+
+		signal(SIGALRM, sigalrm);
+		alarm(1);
+
+		while (1) {
+			DIR *d = opendir(buf);
+			struct dirent *de;
+			while ((de = readdir(d))) {
+				if (strcmp(de->d_name, "0") == 0) {
+					exit(1);
+				}
+			}
+			closedir(d);
+		}
+
+		return 0;
+	} else {
+		perror("fork");
+		return 1;
+	}
+}
diff --git a/tools/testing/selftests/proc/proc-uptime-001.c b/tools/testing/selftests/proc/proc-uptime-001.c
new file mode 100644
index 000000000..f335eec50
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-uptime-001.c
@@ -0,0 +1,58 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that boottime value in /proc/uptime and CLOCK_BOOTTIME increment
+// monotonically. We don't test idle time monotonicity due to broken iowait
+// task counting, cf: comment above get_cpu_idle_time_us()
+#undef NDEBUG
+#include <assert.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "proc-uptime.h"
+
+int main(void)
+{
+	uint64_t start, u0, u1, c0, c1;
+	int fd;
+
+	fd = open("/proc/uptime", O_RDONLY);
+	assert(fd >= 0);
+
+	u0 = proc_uptime(fd);
+	start = u0;
+	c0 = clock_boottime();
+
+	do {
+		u1 = proc_uptime(fd);
+		c1 = clock_boottime();
+
+		/* Is /proc/uptime monotonic ? */
+		assert(u1 >= u0);
+
+		/* Is CLOCK_BOOTTIME monotonic ? */
+		assert(c1 >= c0);
+
+		/* Is CLOCK_BOOTTIME VS /proc/uptime monotonic ? */
+		assert(c0 >= u0);
+
+		u0 = u1;
+		c0 = c1;
+	} while (u1 - start < 100);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-uptime-002.c b/tools/testing/selftests/proc/proc-uptime-002.c
new file mode 100644
index 000000000..ae453daa9
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-uptime-002.c
@@ -0,0 +1,92 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that boottime value in /proc/uptime and CLOCK_BOOTTIME increment
+// monotonically while shifting across CPUs. We don't test idle time
+// monotonicity due to broken iowait task counting, cf: comment above
+// get_cpu_idle_time_us()
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "proc-uptime.h"
+
+static inline int sys_sched_getaffinity(pid_t pid, unsigned int len, unsigned long *m)
+{
+	return syscall(SYS_sched_getaffinity, pid, len, m);
+}
+
+static inline int sys_sched_setaffinity(pid_t pid, unsigned int len, unsigned long *m)
+{
+	return syscall(SYS_sched_setaffinity, pid, len, m);
+}
+
+int main(void)
+{
+	uint64_t u0, u1, c0, c1;
+	unsigned int len;
+	unsigned long *m;
+	unsigned int cpu;
+	int fd;
+
+	/* find out "nr_cpu_ids" */
+	m = NULL;
+	len = 0;
+	do {
+		len += sizeof(unsigned long);
+		free(m);
+		m = malloc(len);
+	} while (sys_sched_getaffinity(0, len, m) == -1 && errno == EINVAL);
+
+	fd = open("/proc/uptime", O_RDONLY);
+	assert(fd >= 0);
+
+	u0 = proc_uptime(fd);
+	c0 = clock_boottime();
+
+	for (cpu = 0; cpu < len * 8; cpu++) {
+		memset(m, 0, len);
+		m[cpu / (8 * sizeof(unsigned long))] |= 1UL << (cpu % (8 * sizeof(unsigned long)));
+
+		/* CPU might not exist, ignore error */
+		sys_sched_setaffinity(0, len, m);
+
+		u1 = proc_uptime(fd);
+		c1 = clock_boottime();
+
+		/* Is /proc/uptime monotonic ? */
+		assert(u1 >= u0);
+
+		/* Is CLOCK_BOOTTIME monotonic ? */
+		assert(c1 >= c0);
+
+		/* Is CLOCK_BOOTTIME VS /proc/uptime monotonic ? */
+		assert(c0 >= u0);
+
+		u0 = u1;
+		c0 = c1;
+	}
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-uptime.h b/tools/testing/selftests/proc/proc-uptime.h
new file mode 100644
index 000000000..730cce4a3
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-uptime.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <time.h>
+
+#include "proc.h"
+
+static uint64_t clock_boottime(void)
+{
+	struct timespec ts;
+	int err;
+
+	err = clock_gettime(CLOCK_BOOTTIME, &ts);
+	assert(err >= 0);
+
+	return (ts.tv_sec * 100) + (ts.tv_nsec / 10000000);
+}
+
+static uint64_t proc_uptime(int fd)
+{
+	uint64_t val1, val2;
+	char buf[64], *p;
+	ssize_t rv;
+
+	/* save "p < end" checks */
+	memset(buf, 0, sizeof(buf));
+	rv = pread(fd, buf, sizeof(buf), 0);
+	assert(0 <= rv && rv <= sizeof(buf));
+	buf[sizeof(buf) - 1] = '\0';
+
+	p = buf;
+
+	val1 = xstrtoull(p, &p);
+	assert(p[0] == '.');
+	assert('0' <= p[1] && p[1] <= '9');
+	assert('0' <= p[2] && p[2] <= '9');
+	assert(p[3] == ' ');
+
+	val2 = (p[1] - '0') * 10 + p[2] - '0';
+
+	return val1 * 100 + val2;
+}
diff --git a/tools/testing/selftests/proc/proc.h b/tools/testing/selftests/proc/proc.h
new file mode 100644
index 000000000..b7d57ea40
--- /dev/null
+++ b/tools/testing/selftests/proc/proc.h
@@ -0,0 +1,51 @@
+#pragma once
+#undef NDEBUG
+#include <assert.h>
+#include <dirent.h>
+#include <errno.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+static inline pid_t sys_getpid(void)
+{
+	return syscall(SYS_getpid);
+}
+
+static inline pid_t sys_gettid(void)
+{
+	return syscall(SYS_gettid);
+}
+
+static inline bool streq(const char *s1, const char *s2)
+{
+	return strcmp(s1, s2) == 0;
+}
+
+static unsigned long long xstrtoull(const char *p, char **end)
+{
+	if (*p == '0') {
+		*end = (char *)p + 1;
+		return 0;
+	} else if ('1' <= *p && *p <= '9') {
+		unsigned long long val;
+
+		errno = 0;
+		val = strtoull(p, end, 10);
+		assert(errno == 0);
+		return val;
+	} else
+		assert(0);
+}
+
+static struct dirent *xreaddir(DIR *d)
+{
+	struct dirent *de;
+
+	errno = 0;
+	de = readdir(d);
+	assert(de || errno == 0);
+	return de;
+}
diff --git a/tools/testing/selftests/proc/read.c b/tools/testing/selftests/proc/read.c
new file mode 100644
index 000000000..35ee78dff
--- /dev/null
+++ b/tools/testing/selftests/proc/read.c
@@ -0,0 +1,148 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test
+// 1) read and lseek on every file in /proc
+// 2) readlink of every symlink in /proc
+// 3) recursively (1) + (2) for every directory in /proc
+// 4) write to /proc/*/clear_refs and /proc/*/task/*/clear_refs
+// 5) write to /proc/sysrq-trigger
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/vfs.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "proc.h"
+
+static void f_reg(DIR *d, const char *filename)
+{
+	char buf[4096];
+	int fd;
+	ssize_t rv;
+
+	/* read from /proc/kmsg can block */
+	fd = openat(dirfd(d), filename, O_RDONLY|O_NONBLOCK);
+	if (fd == -1)
+		return;
+	/* struct proc_ops::proc_lseek is mandatory if file is seekable. */
+	(void)lseek(fd, 0, SEEK_SET);
+	rv = read(fd, buf, sizeof(buf));
+	assert((0 <= rv && rv <= sizeof(buf)) || rv == -1);
+	close(fd);
+}
+
+static void f_reg_write(DIR *d, const char *filename, const char *buf, size_t len)
+{
+	int fd;
+	ssize_t rv;
+
+	fd = openat(dirfd(d), filename, O_WRONLY);
+	if (fd == -1)
+		return;
+	rv = write(fd, buf, len);
+	assert((0 <= rv && rv <= len) || rv == -1);
+	close(fd);
+}
+
+static void f_lnk(DIR *d, const char *filename)
+{
+	char buf[4096];
+	ssize_t rv;
+
+	rv = readlinkat(dirfd(d), filename, buf, sizeof(buf));
+	assert((0 <= rv && rv <= sizeof(buf)) || rv == -1);
+}
+
+static void f(DIR *d, unsigned int level)
+{
+	struct dirent *de;
+
+	de = xreaddir(d);
+	assert(de->d_type == DT_DIR);
+	assert(streq(de->d_name, "."));
+
+	de = xreaddir(d);
+	assert(de->d_type == DT_DIR);
+	assert(streq(de->d_name, ".."));
+
+	while ((de = xreaddir(d))) {
+		assert(!streq(de->d_name, "."));
+		assert(!streq(de->d_name, ".."));
+
+		switch (de->d_type) {
+			DIR *dd;
+			int fd;
+
+		case DT_REG:
+			if (level == 0 && streq(de->d_name, "sysrq-trigger")) {
+				f_reg_write(d, de->d_name, "h", 1);
+			} else if (level == 1 && streq(de->d_name, "clear_refs")) {
+				f_reg_write(d, de->d_name, "1", 1);
+			} else if (level == 3 && streq(de->d_name, "clear_refs")) {
+				f_reg_write(d, de->d_name, "1", 1);
+			} else {
+				f_reg(d, de->d_name);
+			}
+			break;
+		case DT_DIR:
+			fd = openat(dirfd(d), de->d_name, O_DIRECTORY|O_RDONLY);
+			if (fd == -1)
+				continue;
+			dd = fdopendir(fd);
+			if (!dd)
+				continue;
+			f(dd, level + 1);
+			closedir(dd);
+			break;
+		case DT_LNK:
+			f_lnk(d, de->d_name);
+			break;
+		default:
+			assert(0);
+		}
+	}
+}
+
+int main(void)
+{
+	DIR *d;
+	struct statfs sfs;
+
+	d = opendir("/proc");
+	if (!d)
+		return 4;
+
+	/* Ensure /proc is proc. */
+	if (fstatfs(dirfd(d), &sfs) == -1) {
+		return 1;
+	}
+	if (sfs.f_type != 0x9fa0) {
+		fprintf(stderr, "error: unexpected f_type %lx\n", (long)sfs.f_type);
+		return 2;
+	}
+
+	f(d, 0);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/self.c b/tools/testing/selftests/proc/self.c
new file mode 100644
index 000000000..21c15a1ff
--- /dev/null
+++ b/tools/testing/selftests/proc/self.c
@@ -0,0 +1,39 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that /proc/self gives correct TGID.
+#undef NDEBUG
+#include <assert.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "proc.h"
+
+int main(void)
+{
+	char buf1[64], buf2[64];
+	pid_t pid;
+	ssize_t rv;
+
+	pid = sys_getpid();
+	snprintf(buf1, sizeof(buf1), "%u", pid);
+
+	rv = readlink("/proc/self", buf2, sizeof(buf2));
+	assert(rv == strlen(buf1));
+	buf2[rv] = '\0';
+	assert(streq(buf1, buf2));
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/setns-dcache.c b/tools/testing/selftests/proc/setns-dcache.c
new file mode 100644
index 000000000..60ab197a7
--- /dev/null
+++ b/tools/testing/selftests/proc/setns-dcache.c
@@ -0,0 +1,129 @@
+/*
+ * Copyright © 2019 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * Test that setns(CLONE_NEWNET) points to new /proc/net content even
+ * if old one is in dcache.
+ *
+ * FIXME /proc/net/unix is under CONFIG_UNIX which can be disabled.
+ */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/socket.h>
+
+static pid_t pid = -1;
+
+static void f(void)
+{
+	if (pid > 0) {
+		kill(pid, SIGTERM);
+	}
+}
+
+int main(void)
+{
+	int fd[2];
+	char _ = 0;
+	int nsfd;
+
+	atexit(f);
+
+	/* Check for priviledges and syscall availability straight away. */
+	if (unshare(CLONE_NEWNET) == -1) {
+		if (errno == ENOSYS || errno == EPERM) {
+			return 4;
+		}
+		return 1;
+	}
+	/* Distinguisher between two otherwise empty net namespaces. */
+	if (socket(AF_UNIX, SOCK_STREAM, 0) == -1) {
+		return 1;
+	}
+
+	if (pipe(fd) == -1) {
+		return 1;
+	}
+
+	pid = fork();
+	if (pid == -1) {
+		return 1;
+	}
+
+	if (pid == 0) {
+		if (unshare(CLONE_NEWNET) == -1) {
+			return 1;
+		}
+
+		if (write(fd[1], &_, 1) != 1) {
+			return 1;
+		}
+
+		pause();
+
+		return 0;
+	}
+
+	if (read(fd[0], &_, 1) != 1) {
+		return 1;
+	}
+
+	{
+		char buf[64];
+		snprintf(buf, sizeof(buf), "/proc/%u/ns/net", pid);
+		nsfd = open(buf, O_RDONLY);
+		if (nsfd == -1) {
+			return 1;
+		}
+	}
+
+	/* Reliably pin dentry into dcache. */
+	(void)open("/proc/net/unix", O_RDONLY);
+
+	if (setns(nsfd, CLONE_NEWNET) == -1) {
+		return 1;
+	}
+
+	kill(pid, SIGTERM);
+	pid = 0;
+
+	{
+		char buf[4096];
+		ssize_t rv;
+		int fd;
+
+		fd = open("/proc/net/unix", O_RDONLY);
+		if (fd == -1) {
+			return 1;
+		}
+
+#define S "Num       RefCount Protocol Flags    Type St Inode Path\n"
+		rv = read(fd, buf, sizeof(buf));
+
+		assert(rv == strlen(S));
+		assert(memcmp(buf, S, strlen(S)) == 0);
+	}
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/setns-sysvipc.c b/tools/testing/selftests/proc/setns-sysvipc.c
new file mode 100644
index 000000000..903890c5e
--- /dev/null
+++ b/tools/testing/selftests/proc/setns-sysvipc.c
@@ -0,0 +1,133 @@
+/*
+ * Copyright © 2019 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * Test that setns(CLONE_NEWIPC) points to new /proc/sysvipc content even
+ * if old one is in dcache.
+ */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <stdio.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+
+static pid_t pid = -1;
+
+static void f(void)
+{
+	if (pid > 0) {
+		kill(pid, SIGTERM);
+	}
+}
+
+int main(void)
+{
+	int fd[2];
+	char _ = 0;
+	int nsfd;
+
+	atexit(f);
+
+	/* Check for priviledges and syscall availability straight away. */
+	if (unshare(CLONE_NEWIPC) == -1) {
+		if (errno == ENOSYS || errno == EPERM) {
+			return 4;
+		}
+		return 1;
+	}
+	/* Distinguisher between two otherwise empty IPC namespaces. */
+	if (shmget(IPC_PRIVATE, 1, IPC_CREAT) == -1) {
+		return 1;
+	}
+
+	if (pipe(fd) == -1) {
+		return 1;
+	}
+
+	pid = fork();
+	if (pid == -1) {
+		return 1;
+	}
+
+	if (pid == 0) {
+		if (unshare(CLONE_NEWIPC) == -1) {
+			return 1;
+		}
+
+		if (write(fd[1], &_, 1) != 1) {
+			return 1;
+		}
+
+		pause();
+
+		return 0;
+	}
+
+	if (read(fd[0], &_, 1) != 1) {
+		return 1;
+	}
+
+	{
+		char buf[64];
+		snprintf(buf, sizeof(buf), "/proc/%u/ns/ipc", pid);
+		nsfd = open(buf, O_RDONLY);
+		if (nsfd == -1) {
+			return 1;
+		}
+	}
+
+	/* Reliably pin dentry into dcache. */
+	(void)open("/proc/sysvipc/shm", O_RDONLY);
+
+	if (setns(nsfd, CLONE_NEWIPC) == -1) {
+		return 1;
+	}
+
+	kill(pid, SIGTERM);
+	pid = 0;
+
+	{
+		char buf[4096];
+		ssize_t rv;
+		int fd;
+
+		fd = open("/proc/sysvipc/shm", O_RDONLY);
+		if (fd == -1) {
+			return 1;
+		}
+
+#define S32 "       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime        rss       swap\n"
+#define S64 "       key      shmid perms                  size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime                   rss                  swap\n"
+		rv = read(fd, buf, sizeof(buf));
+		if (rv == strlen(S32)) {
+			assert(memcmp(buf, S32, strlen(S32)) == 0);
+		} else if (rv == strlen(S64)) {
+			assert(memcmp(buf, S64, strlen(S64)) == 0);
+		} else {
+			assert(0);
+		}
+	}
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/thread-self.c b/tools/testing/selftests/proc/thread-self.c
new file mode 100644
index 000000000..4b23b39b7
--- /dev/null
+++ b/tools/testing/selftests/proc/thread-self.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that /proc/thread-self gives correct TGID/PID.
+#undef NDEBUG
+#include <assert.h>
+#include <sched.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+#include "proc.h"
+
+int f(void *arg)
+{
+	char buf1[64], buf2[64];
+	pid_t pid, tid;
+	ssize_t rv;
+
+	pid = sys_getpid();
+	tid = sys_gettid();
+	snprintf(buf1, sizeof(buf1), "%u/task/%u", pid, tid);
+
+	rv = readlink("/proc/thread-self", buf2, sizeof(buf2));
+	assert(rv == strlen(buf1));
+	buf2[rv] = '\0';
+	assert(streq(buf1, buf2));
+
+	if (arg)
+		exit(0);
+	return 0;
+}
+
+int main(void)
+{
+	const int PAGE_SIZE = sysconf(_SC_PAGESIZE);
+	pid_t pid;
+	void *stack;
+
+	/* main thread */
+	f((void *)0);
+
+	stack = mmap(NULL, 2 * PAGE_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+	assert(stack != MAP_FAILED);
+	/* side thread */
+	pid = clone(f, stack + PAGE_SIZE, CLONE_THREAD|CLONE_SIGHAND|CLONE_VM, (void *)1);
+	assert(pid > 0);
+	pause();
+
+	return 0;
+}