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.

1 files changed, 237 insertions, 0 deletions

diff --git a/tools/perf/util/comm.c b/tools/perf/util/comm.c
new file mode 100644
index 000000000..9880247a2
--- /dev/null
+++ b/tools/perf/util/comm.c
@@ -0,0 +1,237 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "comm.h"
+#include <errno.h>
+#include <string.h>
+#include <internal/rc_check.h>
+#include <linux/refcount.h>
+#include <linux/zalloc.h>
+#include <tools/libc_compat.h> // reallocarray
+
+#include "rwsem.h"
+
+DECLARE_RC_STRUCT(comm_str) {
+	refcount_t refcnt;
+	char str[];
+};
+
+static struct comm_strs {
+	struct rw_semaphore lock;
+	struct comm_str **strs;
+	int num_strs;
+	int capacity;
+} _comm_strs;
+
+static void comm_strs__remove_if_last(struct comm_str *cs);
+
+static void comm_strs__init(void)
+	NO_THREAD_SAFETY_ANALYSIS /* Inherently single threaded due to pthread_once. */
+{
+	init_rwsem(&_comm_strs.lock);
+	_comm_strs.capacity = 16;
+	_comm_strs.num_strs = 0;
+	_comm_strs.strs = calloc(16, sizeof(*_comm_strs.strs));
+}
+
+static struct comm_strs *comm_strs__get(void)
+{
+	static pthread_once_t comm_strs_type_once = PTHREAD_ONCE_INIT;
+
+	pthread_once(&comm_strs_type_once, comm_strs__init);
+
+	return &_comm_strs;
+}
+
+static refcount_t *comm_str__refcnt(struct comm_str *cs)
+{
+	return &RC_CHK_ACCESS(cs)->refcnt;
+}
+
+static const char *comm_str__str(const struct comm_str *cs)
+{
+	return &RC_CHK_ACCESS(cs)->str[0];
+}
+
+static struct comm_str *comm_str__get(struct comm_str *cs)
+{
+	struct comm_str *result;
+
+	if (RC_CHK_GET(result, cs))
+		refcount_inc_not_zero(comm_str__refcnt(cs));
+
+	return result;
+}
+
+static void comm_str__put(struct comm_str *cs)
+{
+	if (!cs)
+		return;
+
+	if (refcount_dec_and_test(comm_str__refcnt(cs))) {
+		RC_CHK_FREE(cs);
+	} else {
+		if (refcount_read(comm_str__refcnt(cs)) == 1)
+			comm_strs__remove_if_last(cs);
+
+		RC_CHK_PUT(cs);
+	}
+}
+
+static struct comm_str *comm_str__new(const char *str)
+{
+	struct comm_str *result = NULL;
+	RC_STRUCT(comm_str) *cs;
+
+	cs = malloc(sizeof(*cs) + strlen(str) + 1);
+	if (ADD_RC_CHK(result, cs)) {
+		refcount_set(comm_str__refcnt(result), 1);
+		strcpy(&cs->str[0], str);
+	}
+	return result;
+}
+
+static int comm_str__search(const void *_key, const void *_member)
+{
+	const char *key = _key;
+	const struct comm_str *member = *(const struct comm_str * const *)_member;
+
+	return strcmp(key, comm_str__str(member));
+}
+
+static void comm_strs__remove_if_last(struct comm_str *cs)
+{
+	struct comm_strs *comm_strs = comm_strs__get();
+
+	down_write(&comm_strs->lock);
+	/*
+	 * Are there only references from the array, if so remove the array
+	 * reference under the write lock so that we don't race with findnew.
+	 */
+	if (refcount_read(comm_str__refcnt(cs)) == 1) {
+		struct comm_str **entry;
+
+		entry = bsearch(comm_str__str(cs), comm_strs->strs, comm_strs->num_strs,
+				sizeof(struct comm_str *), comm_str__search);
+		comm_str__put(*entry);
+		for (int i = entry - comm_strs->strs; i < comm_strs->num_strs - 1; i++)
+			comm_strs->strs[i] = comm_strs->strs[i + 1];
+		comm_strs->num_strs--;
+	}
+	up_write(&comm_strs->lock);
+}
+
+static struct comm_str *__comm_strs__find(struct comm_strs *comm_strs, const char *str)
+	SHARED_LOCKS_REQUIRED(comm_strs->lock)
+{
+	struct comm_str **result;
+
+	result = bsearch(str, comm_strs->strs, comm_strs->num_strs, sizeof(struct comm_str *),
+			 comm_str__search);
+
+	if (!result)
+		return NULL;
+
+	return comm_str__get(*result);
+}
+
+static struct comm_str *comm_strs__findnew(const char *str)
+{
+	struct comm_strs *comm_strs = comm_strs__get();
+	struct comm_str *result;
+
+	if (!comm_strs)
+		return NULL;
+
+	down_read(&comm_strs->lock);
+	result = __comm_strs__find(comm_strs, str);
+	up_read(&comm_strs->lock);
+	if (result)
+		return result;
+
+	down_write(&comm_strs->lock);
+	result = __comm_strs__find(comm_strs, str);
+	if (!result) {
+		if (comm_strs->num_strs == comm_strs->capacity) {
+			struct comm_str **tmp;
+
+			tmp = reallocarray(comm_strs->strs,
+					   comm_strs->capacity + 16,
+					   sizeof(*comm_strs->strs));
+			if (!tmp) {
+				up_write(&comm_strs->lock);
+				return NULL;
+			}
+			comm_strs->strs = tmp;
+			comm_strs->capacity += 16;
+		}
+		result = comm_str__new(str);
+		if (result) {
+			int low = 0, high = comm_strs->num_strs - 1;
+			int insert = comm_strs->num_strs; /* Default to inserting at the end. */
+
+			while (low <= high) {
+				int mid = low + (high - low) / 2;
+				int cmp = strcmp(comm_str__str(comm_strs->strs[mid]), str);
+
+				if (cmp < 0) {
+					low = mid + 1;
+				} else {
+					high = mid - 1;
+					insert = mid;
+				}
+			}
+			memmove(&comm_strs->strs[insert + 1], &comm_strs->strs[insert],
+				(comm_strs->num_strs - insert) * sizeof(struct comm_str *));
+			comm_strs->num_strs++;
+			comm_strs->strs[insert] = result;
+		}
+	}
+	up_write(&comm_strs->lock);
+	return comm_str__get(result);
+}
+
+struct comm *comm__new(const char *str, u64 timestamp, bool exec)
+{
+	struct comm *comm = zalloc(sizeof(*comm));
+
+	if (!comm)
+		return NULL;
+
+	comm->start = timestamp;
+	comm->exec = exec;
+
+	comm->comm_str = comm_strs__findnew(str);
+	if (!comm->comm_str) {
+		free(comm);
+		return NULL;
+	}
+
+	return comm;
+}
+
+int comm__override(struct comm *comm, const char *str, u64 timestamp, bool exec)
+{
+	struct comm_str *new, *old = comm->comm_str;
+
+	new = comm_strs__findnew(str);
+	if (!new)
+		return -ENOMEM;
+
+	comm_str__put(old);
+	comm->comm_str = new;
+	comm->start = timestamp;
+	if (exec)
+		comm->exec = true;
+
+	return 0;
+}
+
+void comm__free(struct comm *comm)
+{
+	comm_str__put(comm->comm_str);
+	free(comm);
+}
+
+const char *comm__str(const struct comm *comm)
+{
+	return comm_str__str(comm->comm_str);
+}