Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a', 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into HEADgrafted

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.

4 files changed, 334 insertions, 0 deletions

diff --git a/tools/testing/selftests/ring-buffer/.gitignore b/tools/testing/selftests/ring-buffer/.gitignore
new file mode 100644
index 000000000..3aed1a2a6
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/.gitignore
@@ -0,0 +1 @@
+map_test
diff --git a/tools/testing/selftests/ring-buffer/Makefile b/tools/testing/selftests/ring-buffer/Makefile
new file mode 100644
index 000000000..236057826
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += -Wl,-no-as-needed -Wall
+CFLAGS += $(KHDR_INCLUDES)
+
+TEST_GEN_PROGS = map_test
+
+include ../lib.mk
diff --git a/tools/testing/selftests/ring-buffer/config b/tools/testing/selftests/ring-buffer/config
new file mode 100644
index 000000000..d936f8f00
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/config
@@ -0,0 +1,2 @@
+CONFIG_FTRACE=y
+CONFIG_TRACER_SNAPSHOT=y
diff --git a/tools/testing/selftests/ring-buffer/map_test.c b/tools/testing/selftests/ring-buffer/map_test.c
new file mode 100644
index 000000000..f24677737
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/map_test.c
@@ -0,0 +1,324 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Ring-buffer memory mapping tests
+ *
+ * Copyright (c) 2024 Vincent Donnefort <vdonnefort@google.com>
+ */
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <linux/trace_mmap.h>
+
+#include <sys/mman.h>
+#include <sys/ioctl.h>
+
+#include "../user_events/user_events_selftests.h" /* share tracefs setup */
+#include "kselftest_harness.h"
+
+#define TRACEFS_ROOT "/sys/kernel/tracing"
+
+static int __tracefs_write(const char *path, const char *value)
+{
+	int fd, ret;
+
+	fd = open(path, O_WRONLY | O_TRUNC);
+	if (fd < 0)
+		return fd;
+
+	ret = write(fd, value, strlen(value));
+
+	close(fd);
+
+	return ret == -1 ? -errno : 0;
+}
+
+static int __tracefs_write_int(const char *path, int value)
+{
+	char *str;
+	int ret;
+
+	if (asprintf(&str, "%d", value) < 0)
+		return -1;
+
+	ret = __tracefs_write(path, str);
+
+	free(str);
+
+	return ret;
+}
+
+#define tracefs_write_int(path, value) \
+	ASSERT_EQ(__tracefs_write_int((path), (value)), 0)
+
+#define tracefs_write(path, value) \
+	ASSERT_EQ(__tracefs_write((path), (value)), 0)
+
+static int tracefs_reset(void)
+{
+	if (__tracefs_write_int(TRACEFS_ROOT"/tracing_on", 0))
+		return -1;
+	if (__tracefs_write(TRACEFS_ROOT"/trace", ""))
+		return -1;
+	if (__tracefs_write(TRACEFS_ROOT"/set_event", ""))
+		return -1;
+	if (__tracefs_write(TRACEFS_ROOT"/current_tracer", "nop"))
+		return -1;
+
+	return 0;
+}
+
+struct tracefs_cpu_map_desc {
+	struct trace_buffer_meta	*meta;
+	int				cpu_fd;
+};
+
+int tracefs_cpu_map(struct tracefs_cpu_map_desc *desc, int cpu)
+{
+	int page_size = getpagesize();
+	char *cpu_path;
+	void *map;
+
+	if (asprintf(&cpu_path,
+		     TRACEFS_ROOT"/per_cpu/cpu%d/trace_pipe_raw",
+		     cpu) < 0)
+		return -ENOMEM;
+
+	desc->cpu_fd = open(cpu_path, O_RDONLY | O_NONBLOCK);
+	free(cpu_path);
+	if (desc->cpu_fd < 0)
+		return -ENODEV;
+
+again:
+	map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, desc->cpu_fd, 0);
+	if (map == MAP_FAILED)
+		return -errno;
+
+	desc->meta = (struct trace_buffer_meta *)map;
+
+	/* the meta-page is bigger than the original mapping */
+	if (page_size < desc->meta->meta_struct_len) {
+		int meta_page_size = desc->meta->meta_page_size;
+
+		munmap(desc->meta, page_size);
+		page_size = meta_page_size;
+		goto again;
+	}
+
+	return 0;
+}
+
+void tracefs_cpu_unmap(struct tracefs_cpu_map_desc *desc)
+{
+	munmap(desc->meta, desc->meta->meta_page_size);
+	close(desc->cpu_fd);
+}
+
+FIXTURE(map) {
+	struct tracefs_cpu_map_desc	map_desc;
+	bool				umount;
+};
+
+FIXTURE_VARIANT(map) {
+	int	subbuf_size;
+};
+
+FIXTURE_VARIANT_ADD(map, subbuf_size_4k) {
+	.subbuf_size = 4,
+};
+
+FIXTURE_VARIANT_ADD(map, subbuf_size_8k) {
+	.subbuf_size = 8,
+};
+
+FIXTURE_SETUP(map)
+{
+	int cpu = sched_getcpu();
+	cpu_set_t cpu_mask;
+	bool fail, umount;
+	char *message;
+
+	if (getuid() != 0)
+		SKIP(return, "Skipping: %s", "Please run the test as root");
+
+	if (!tracefs_enabled(&message, &fail, &umount)) {
+		if (fail) {
+			TH_LOG("Tracefs setup failed: %s", message);
+			ASSERT_FALSE(fail);
+		}
+		SKIP(return, "Skipping: %s", message);
+	}
+
+	self->umount = umount;
+
+	ASSERT_GE(cpu, 0);
+
+	ASSERT_EQ(tracefs_reset(), 0);
+
+	tracefs_write_int(TRACEFS_ROOT"/buffer_subbuf_size_kb", variant->subbuf_size);
+
+	ASSERT_EQ(tracefs_cpu_map(&self->map_desc, cpu), 0);
+
+	/*
+	 * Ensure generated events will be found on this very same ring-buffer.
+	 */
+	CPU_ZERO(&cpu_mask);
+	CPU_SET(cpu, &cpu_mask);
+	ASSERT_EQ(sched_setaffinity(0, sizeof(cpu_mask), &cpu_mask), 0);
+}
+
+FIXTURE_TEARDOWN(map)
+{
+	tracefs_reset();
+
+	if (self->umount)
+		tracefs_unmount();
+
+	tracefs_cpu_unmap(&self->map_desc);
+}
+
+TEST_F(map, meta_page_check)
+{
+	struct tracefs_cpu_map_desc *desc = &self->map_desc;
+	int cnt = 0;
+
+	ASSERT_EQ(desc->meta->entries, 0);
+	ASSERT_EQ(desc->meta->overrun, 0);
+	ASSERT_EQ(desc->meta->read, 0);
+
+	ASSERT_EQ(desc->meta->reader.id, 0);
+	ASSERT_EQ(desc->meta->reader.read, 0);
+
+	ASSERT_EQ(ioctl(desc->cpu_fd, TRACE_MMAP_IOCTL_GET_READER), 0);
+	ASSERT_EQ(desc->meta->reader.id, 0);
+
+	tracefs_write_int(TRACEFS_ROOT"/tracing_on", 1);
+	for (int i = 0; i < 16; i++)
+		tracefs_write_int(TRACEFS_ROOT"/trace_marker", i);
+again:
+	ASSERT_EQ(ioctl(desc->cpu_fd, TRACE_MMAP_IOCTL_GET_READER), 0);
+
+	ASSERT_EQ(desc->meta->entries, 16);
+	ASSERT_EQ(desc->meta->overrun, 0);
+	ASSERT_EQ(desc->meta->read, 16);
+
+	ASSERT_EQ(desc->meta->reader.id, 1);
+
+	if (!(cnt++))
+		goto again;
+}
+
+TEST_F(map, data_mmap)
+{
+	struct tracefs_cpu_map_desc *desc = &self->map_desc;
+	unsigned long meta_len, data_len;
+	void *data;
+
+	meta_len = desc->meta->meta_page_size;
+	data_len = desc->meta->subbuf_size * desc->meta->nr_subbufs;
+
+	/* Map all the available subbufs */
+	data = mmap(NULL, data_len, PROT_READ, MAP_SHARED,
+		    desc->cpu_fd, meta_len);
+	ASSERT_NE(data, MAP_FAILED);
+	munmap(data, data_len);
+
+	/* Map all the available subbufs - 1 */
+	data_len -= desc->meta->subbuf_size;
+	data = mmap(NULL, data_len, PROT_READ, MAP_SHARED,
+		    desc->cpu_fd, meta_len);
+	ASSERT_NE(data, MAP_FAILED);
+	munmap(data, data_len);
+
+	/* Offset within ring-buffer bounds, mapping size overflow */
+	meta_len += desc->meta->subbuf_size * 2;
+	data = mmap(NULL, data_len, PROT_READ, MAP_SHARED,
+		    desc->cpu_fd, meta_len);
+	ASSERT_EQ(data, MAP_FAILED);
+
+	/* Offset outside ring-buffer bounds */
+	data_len = desc->meta->subbuf_size * desc->meta->nr_subbufs;
+	data = mmap(NULL, data_len, PROT_READ, MAP_SHARED,
+		    desc->cpu_fd, data_len + (desc->meta->subbuf_size * 2));
+	ASSERT_EQ(data, MAP_FAILED);
+
+	/* Verify meta-page padding */
+	if (desc->meta->meta_page_size > getpagesize()) {
+		data_len = desc->meta->meta_page_size;
+		data = mmap(NULL, data_len,
+			    PROT_READ, MAP_SHARED, desc->cpu_fd, 0);
+		ASSERT_NE(data, MAP_FAILED);
+
+		for (int i = desc->meta->meta_struct_len;
+		     i < desc->meta->meta_page_size; i += sizeof(int))
+			ASSERT_EQ(*(int *)(data + i), 0);
+
+		munmap(data, data_len);
+	}
+}
+
+FIXTURE(snapshot) {
+	bool	umount;
+};
+
+FIXTURE_SETUP(snapshot)
+{
+	bool fail, umount;
+	struct stat sb;
+	char *message;
+
+	if (getuid() != 0)
+		SKIP(return, "Skipping: %s", "Please run the test as root");
+
+	if (stat(TRACEFS_ROOT"/snapshot", &sb))
+		SKIP(return, "Skipping: %s", "snapshot not available");
+
+	if (!tracefs_enabled(&message, &fail, &umount)) {
+		if (fail) {
+			TH_LOG("Tracefs setup failed: %s", message);
+			ASSERT_FALSE(fail);
+		}
+		SKIP(return, "Skipping: %s", message);
+	}
+
+	self->umount = umount;
+}
+
+FIXTURE_TEARDOWN(snapshot)
+{
+	__tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+			"!snapshot");
+	tracefs_reset();
+
+	if (self->umount)
+		tracefs_unmount();
+}
+
+TEST_F(snapshot, excludes_map)
+{
+	struct tracefs_cpu_map_desc map_desc;
+	int cpu = sched_getcpu();
+
+	ASSERT_GE(cpu, 0);
+	tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+		      "snapshot");
+	ASSERT_EQ(tracefs_cpu_map(&map_desc, cpu), -EBUSY);
+}
+
+TEST_F(snapshot, excluded_by_map)
+{
+	struct tracefs_cpu_map_desc map_desc;
+	int cpu = sched_getcpu();
+
+	ASSERT_EQ(tracefs_cpu_map(&map_desc, cpu), 0);
+
+	ASSERT_EQ(__tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+				  "snapshot"), -EBUSY);
+	ASSERT_EQ(__tracefs_write(TRACEFS_ROOT"/snapshot",
+				  "1"), -EBUSY);
+}
+
+TEST_HARNESS_MAIN