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.

3 files changed, 29 insertions, 0 deletions

diff --git a/samples/watchdog/.gitignore b/samples/watchdog/.gitignore
new file mode 100644
index 000000000..a70a0150e
--- /dev/null
+++ b/samples/watchdog/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/watchdog-simple
diff --git a/samples/watchdog/Makefile b/samples/watchdog/Makefile
new file mode 100644
index 000000000..ab39d23dc
--- /dev/null
+++ b/samples/watchdog/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0
+userprogs-always-y += watchdog-simple
diff --git a/samples/watchdog/watchdog-simple.c b/samples/watchdog/watchdog-simple.c
new file mode 100644
index 000000000..9ce66d2ca
--- /dev/null
+++ b/samples/watchdog/watchdog-simple.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+int main(void)
+{
+	int fd = open("/dev/watchdog", O_WRONLY);
+	int ret = 0;
+	if (fd == -1) {
+		perror("watchdog");
+		exit(EXIT_FAILURE);
+	}
+	while (1) {
+		ret = write(fd, "\0", 1);
+		if (ret != 1) {
+			ret = -1;
+			break;
+		}
+		sleep(10);
+	}
+	close(fd);
+	return ret;
+}