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, 165 insertions, 0 deletions

diff --git a/fs/jffs2/background.c b/fs/jffs2/background.c
new file mode 100644
index 000000000..bb0ee1a59
--- /dev/null
+++ b/fs/jffs2/background.c
@@ -0,0 +1,165 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
+ *
+ * Created by David Woodhouse <dwmw2@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/jffs2.h>
+#include <linux/mtd/mtd.h>
+#include <linux/completion.h>
+#include <linux/sched/signal.h>
+#include <linux/freezer.h>
+#include <linux/kthread.h>
+#include "nodelist.h"
+
+
+static int jffs2_garbage_collect_thread(void *);
+
+void jffs2_garbage_collect_trigger(struct jffs2_sb_info *c)
+{
+	assert_spin_locked(&c->erase_completion_lock);
+	if (c->gc_task && jffs2_thread_should_wake(c))
+		send_sig(SIGHUP, c->gc_task, 1);
+}
+
+/* This must only ever be called when no GC thread is currently running */
+int jffs2_start_garbage_collect_thread(struct jffs2_sb_info *c)
+{
+	struct task_struct *tsk;
+	int ret = 0;
+
+	BUG_ON(c->gc_task);
+
+	init_completion(&c->gc_thread_start);
+	init_completion(&c->gc_thread_exit);
+
+	tsk = kthread_run(jffs2_garbage_collect_thread, c, "jffs2_gcd_mtd%d", c->mtd->index);
+	if (IS_ERR(tsk)) {
+		pr_warn("fork failed for JFFS2 garbage collect thread: %pe\n",
+			tsk);
+		complete(&c->gc_thread_exit);
+		ret = PTR_ERR(tsk);
+	} else {
+		/* Wait for it... */
+		jffs2_dbg(1, "Garbage collect thread is pid %d\n", tsk->pid);
+		wait_for_completion(&c->gc_thread_start);
+		ret = tsk->pid;
+	}
+
+	return ret;
+}
+
+void jffs2_stop_garbage_collect_thread(struct jffs2_sb_info *c)
+{
+	int wait = 0;
+	spin_lock(&c->erase_completion_lock);
+	if (c->gc_task) {
+		jffs2_dbg(1, "Killing GC task %d\n", c->gc_task->pid);
+		send_sig(SIGKILL, c->gc_task, 1);
+		wait = 1;
+	}
+	spin_unlock(&c->erase_completion_lock);
+	if (wait)
+		wait_for_completion(&c->gc_thread_exit);
+}
+
+static int jffs2_garbage_collect_thread(void *_c)
+{
+	struct jffs2_sb_info *c = _c;
+	sigset_t hupmask;
+
+	siginitset(&hupmask, sigmask(SIGHUP));
+	allow_signal(SIGKILL);
+	allow_signal(SIGSTOP);
+	allow_signal(SIGHUP);
+
+	c->gc_task = current;
+	complete(&c->gc_thread_start);
+
+	set_user_nice(current, 10);
+
+	set_freezable();
+	for (;;) {
+		sigprocmask(SIG_UNBLOCK, &hupmask, NULL);
+	again:
+		spin_lock(&c->erase_completion_lock);
+		if (!jffs2_thread_should_wake(c)) {
+			set_current_state (TASK_INTERRUPTIBLE);
+			spin_unlock(&c->erase_completion_lock);
+			jffs2_dbg(1, "%s(): sleeping...\n", __func__);
+			schedule();
+		} else {
+			spin_unlock(&c->erase_completion_lock);
+		}
+		/* Problem - immediately after bootup, the GCD spends a lot
+		 * of time in places like jffs2_kill_fragtree(); so much so
+		 * that userspace processes (like gdm and X) are starved
+		 * despite plenty of cond_resched()s and renicing.  Yield()
+		 * doesn't help, either (presumably because userspace and GCD
+		 * are generally competing for a higher latency resource -
+		 * disk).
+		 * This forces the GCD to slow the hell down.   Pulling an
+		 * inode in with read_inode() is much preferable to having
+		 * the GC thread get there first. */
+		schedule_timeout_interruptible(msecs_to_jiffies(50));
+
+		if (kthread_should_stop()) {
+			jffs2_dbg(1, "%s(): kthread_stop() called\n", __func__);
+			goto die;
+		}
+
+		/* Put_super will send a SIGKILL and then wait on the sem.
+		 */
+		while (signal_pending(current) || freezing(current)) {
+			unsigned long signr;
+
+			if (try_to_freeze())
+				goto again;
+
+			signr = kernel_dequeue_signal();
+
+			switch(signr) {
+			case SIGSTOP:
+				jffs2_dbg(1, "%s(): SIGSTOP received\n",
+					  __func__);
+				kernel_signal_stop();
+				break;
+
+			case SIGKILL:
+				jffs2_dbg(1, "%s(): SIGKILL received\n",
+					  __func__);
+				goto die;
+
+			case SIGHUP:
+				jffs2_dbg(1, "%s(): SIGHUP received\n",
+					  __func__);
+				break;
+			default:
+				jffs2_dbg(1, "%s(): signal %ld received\n",
+					  __func__, signr);
+			}
+		}
+		/* We don't want SIGHUP to interrupt us. STOP and KILL are OK though. */
+		sigprocmask(SIG_BLOCK, &hupmask, NULL);
+
+		jffs2_dbg(1, "%s(): pass\n", __func__);
+		if (jffs2_garbage_collect_pass(c) == -ENOSPC) {
+			pr_notice("No space for garbage collection. Aborting GC thread\n");
+			goto die;
+		}
+	}
+ die:
+	spin_lock(&c->erase_completion_lock);
+	c->gc_task = NULL;
+	spin_unlock(&c->erase_completion_lock);
+	kthread_complete_and_exit(&c->gc_thread_exit, 0);
+}