ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 180 insertions, 0 deletions

diff --git a/tools/testing/selftests/kcmp/.gitignore b/tools/testing/selftests/kcmp/.gitignore
new file mode 100644
index 000000000..38ccdfe80
--- /dev/null
+++ b/tools/testing/selftests/kcmp/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+kcmp_test
+kcmp-test-file
diff --git a/tools/testing/selftests/kcmp/Makefile b/tools/testing/selftests/kcmp/Makefile
new file mode 100644
index 000000000..59a1e5379
--- /dev/null
+++ b/tools/testing/selftests/kcmp/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-only
+CFLAGS += $(KHDR_INCLUDES)
+
+TEST_GEN_PROGS := kcmp_test
+
+EXTRA_CLEAN := $(OUTPUT)/kcmp-test-file
+
+include ../lib.mk
+
diff --git a/tools/testing/selftests/kcmp/kcmp_test.c b/tools/testing/selftests/kcmp/kcmp_test.c
new file mode 100644
index 000000000..79aa438b7
--- /dev/null
+++ b/tools/testing/selftests/kcmp/kcmp_test.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <limits.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <fcntl.h>
+#include <linux/unistd.h>
+#include <linux/kcmp.h>
+
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/epoll.h>
+
+#include "kselftest.h"
+
+static long sys_kcmp(int pid1, int pid2, int type, unsigned long fd1, unsigned long fd2)
+{
+	return syscall(__NR_kcmp, pid1, pid2, type, fd1, fd2);
+}
+
+static const unsigned int duped_num = 64;
+
+int main(int argc, char **argv)
+{
+	const char kpath[] = "kcmp-test-file";
+	struct kcmp_epoll_slot epoll_slot;
+	struct epoll_event ev;
+	int pid1, pid2;
+	int pipefd[2];
+	int fd1, fd2;
+	int epollfd;
+	int status;
+	int fddup;
+
+	fd1 = open(kpath, O_RDWR | O_CREAT | O_TRUNC, 0644);
+	pid1 = getpid();
+
+	if (fd1 < 0) {
+		perror("Can't create file");
+		ksft_exit_fail();
+	}
+
+	if (pipe(pipefd)) {
+		perror("Can't create pipe");
+		ksft_exit_fail();
+	}
+
+	epollfd = epoll_create1(0);
+	if (epollfd < 0) {
+		perror("epoll_create1 failed");
+		ksft_exit_fail();
+	}
+
+	memset(&ev, 0xff, sizeof(ev));
+	ev.events = EPOLLIN | EPOLLOUT;
+
+	if (epoll_ctl(epollfd, EPOLL_CTL_ADD, pipefd[0], &ev)) {
+		perror("epoll_ctl failed");
+		ksft_exit_fail();
+	}
+
+	fddup = dup2(pipefd[1], duped_num);
+	if (fddup < 0) {
+		perror("dup2 failed");
+		ksft_exit_fail();
+	}
+
+	if (epoll_ctl(epollfd, EPOLL_CTL_ADD, fddup, &ev)) {
+		perror("epoll_ctl failed");
+		ksft_exit_fail();
+	}
+	close(fddup);
+
+	pid2 = fork();
+	if (pid2 < 0) {
+		perror("fork failed");
+		ksft_exit_fail();
+	}
+
+	if (!pid2) {
+		int pid2 = getpid();
+		int ret;
+
+		ksft_print_header();
+		ksft_set_plan(3);
+
+		fd2 = open(kpath, O_RDWR);
+		if (fd2 < 0) {
+			perror("Can't open file");
+			ksft_exit_fail();
+		}
+
+		/* An example of output and arguments */
+		printf("pid1: %6d pid2: %6d FD: %2ld FILES: %2ld VM: %2ld "
+		       "FS: %2ld SIGHAND: %2ld IO: %2ld SYSVSEM: %2ld "
+		       "INV: %2ld\n",
+		       pid1, pid2,
+		       sys_kcmp(pid1, pid2, KCMP_FILE,		fd1, fd2),
+		       sys_kcmp(pid1, pid2, KCMP_FILES,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_VM,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_FS,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_SIGHAND,	0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_IO,		0, 0),
+		       sys_kcmp(pid1, pid2, KCMP_SYSVSEM,	0, 0),
+
+			/* This one should fail */
+		       sys_kcmp(pid1, pid2, KCMP_TYPES + 1,	0, 0));
+
+		/* This one should return same fd */
+		ret = sys_kcmp(pid1, pid2, KCMP_FILE, fd1, fd1);
+		if (ret) {
+			printf("FAIL: 0 expected but %d returned (%s)\n",
+				ret, strerror(errno));
+			ksft_inc_fail_cnt();
+			ret = -1;
+		} else {
+			printf("PASS: 0 returned as expected\n");
+			ksft_inc_pass_cnt();
+		}
+
+		/* Compare with self */
+		ret = sys_kcmp(pid1, pid1, KCMP_VM, 0, 0);
+		if (ret) {
+			printf("FAIL: 0 expected but %d returned (%s)\n",
+				ret, strerror(errno));
+			ksft_inc_fail_cnt();
+			ret = -1;
+		} else {
+			printf("PASS: 0 returned as expected\n");
+			ksft_inc_pass_cnt();
+		}
+
+		/* Compare epoll target */
+		epoll_slot = (struct kcmp_epoll_slot) {
+			.efd	= epollfd,
+			.tfd	= duped_num,
+			.toff	= 0,
+		};
+		ret = sys_kcmp(pid1, pid1, KCMP_EPOLL_TFD, pipefd[1],
+			       (unsigned long)(void *)&epoll_slot);
+		if (ret) {
+			printf("FAIL: 0 expected but %d returned (%s)\n",
+				ret, strerror(errno));
+			ksft_inc_fail_cnt();
+			ret = -1;
+		} else {
+			printf("PASS: 0 returned as expected\n");
+			ksft_inc_pass_cnt();
+		}
+
+
+		if (ret)
+			ksft_exit_fail();
+		else
+			ksft_exit_pass();
+	}
+
+	waitpid(pid2, &status, P_ALL);
+
+	return 0;
+}