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.

2 files changed, 166 insertions, 0 deletions

diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
new file mode 100644
index 000000000..86036f1a2
--- /dev/null
+++ b/samples/hung_task/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_tests.o
diff --git a/samples/hung_task/hung_task_tests.c b/samples/hung_task/hung_task_tests.c
new file mode 100644
index 000000000..0360ec916
--- /dev/null
+++ b/samples/hung_task/hung_task_tests.c
@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * hung_task_tests.c - Sample code for testing hung tasks with mutex,
+ * semaphore, etc.
+ *
+ * Usage: Load this module and read `<debugfs>/hung_task/mutex`,
+ *        `<debugfs>/hung_task/semaphore`, `<debugfs>/hung_task/rw_semaphore_read`,
+ *        `<debugfs>/hung_task/rw_semaphore_write`, etc., with 2 or more processes.
+ *
+ * This is for testing kernel hung_task error messages with various locking
+ * mechanisms (e.g., mutex, semaphore, rw_semaphore_read, rw_semaphore_write, etc.).
+ * Note that this may freeze your system or cause a panic. Use only for testing purposes.
+ */
+
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/semaphore.h>
+#include <linux/rwsem.h>
+
+#define HUNG_TASK_DIR			"hung_task"
+#define HUNG_TASK_MUTEX_FILE		"mutex"
+#define HUNG_TASK_SEM_FILE		"semaphore"
+#define HUNG_TASK_RWSEM_READ_FILE	"rw_semaphore_read"
+#define HUNG_TASK_RWSEM_WRITE_FILE	"rw_semaphore_write"
+#define SLEEP_SECOND			256
+
+static const char dummy_string[] = "This is a dummy string.";
+static DEFINE_MUTEX(dummy_mutex);
+static DEFINE_SEMAPHORE(dummy_sem, 1);
+static DECLARE_RWSEM(dummy_rwsem);
+static struct dentry *hung_task_dir;
+
+/* Mutex-based read function */
+static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf,
+				size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Second task waits on mutex, entering uninterruptible sleep */
+	guard(mutex)(&dummy_mutex);
+
+	/* First task sleeps here, interruptible */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* Semaphore-based read function */
+static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf,
+				    size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Second task waits on semaphore, entering uninterruptible sleep */
+	down(&dummy_sem);
+
+	/* First task sleeps here, interruptible */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	up(&dummy_sem);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* Read-write semaphore read function */
+static ssize_t read_dummy_rwsem_read(struct file *file, char __user *user_buf,
+				     size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Acquires read lock, allowing concurrent readers but blocks if write lock is held */
+	down_read(&dummy_rwsem);
+
+	/* Sleeps here, potentially triggering hung task detection if lock is held too long */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	up_read(&dummy_rwsem);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* Read-write semaphore write function */
+static ssize_t read_dummy_rwsem_write(struct file *file, char __user *user_buf,
+				      size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Acquires exclusive write lock, blocking all other readers and writers */
+	down_write(&dummy_rwsem);
+
+	/* Sleeps here, potentially triggering hung task detection if lock is held too long */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	up_write(&dummy_rwsem);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* File operations for mutex */
+static const struct file_operations hung_task_mutex_fops = {
+	.read = read_dummy_mutex,
+};
+
+/* File operations for semaphore */
+static const struct file_operations hung_task_sem_fops = {
+	.read = read_dummy_semaphore,
+};
+
+/* File operations for rw_semaphore read */
+static const struct file_operations hung_task_rwsem_read_fops = {
+	.read = read_dummy_rwsem_read,
+};
+
+/* File operations for rw_semaphore write */
+static const struct file_operations hung_task_rwsem_write_fops = {
+	.read = read_dummy_rwsem_write,
+};
+
+static int __init hung_task_tests_init(void)
+{
+	hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
+	if (IS_ERR(hung_task_dir))
+		return PTR_ERR(hung_task_dir);
+
+	/* Create debugfs files for mutex and semaphore tests */
+	debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_mutex_fops);
+	debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_sem_fops);
+	debugfs_create_file(HUNG_TASK_RWSEM_READ_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_rwsem_read_fops);
+	debugfs_create_file(HUNG_TASK_RWSEM_WRITE_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_rwsem_write_fops);
+
+	return 0;
+}
+
+static void __exit hung_task_tests_exit(void)
+{
+	debugfs_remove_recursive(hung_task_dir);
+}
+
+module_init(hung_task_tests_init);
+module_exit(hung_task_tests_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Masami Hiramatsu <mhiramat@kernel.org>");
+MODULE_AUTHOR("Zi Li <amaindex@outlook.com>");
+MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task");