Re: [syzbot] [reiserfs?] possible deadlock in __run_timers

[Lizhi Xu]

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 88035e5694a8

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 2989b57e154a..b7f3525bedb0 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -941,8 +941,12 @@ static void worker_enter_idle(struct worker *worker)
 	/* idle_list is LIFO */
 	list_add(&worker->entry, &pool->idle_list);
 
-	if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
+	if (too_many_workers(pool) && !timer_pending(&pool->idle_timer)) {
+		unsigned long flags;
+		raw_spin_unlock_irqrestore(&pool->lock, flags);
 		mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);
+		raw_spin_lock_irqsave(&pool->lock, flags);
+	}
 
 	/* Sanity check nr_running. */
 	WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running);
@@ -2164,6 +2168,7 @@ static struct worker *create_worker(struct worker_pool *pool)
 	struct worker *worker;
 	int id;
 	char id_buf[23];
+	unsigned long flags;
 
 	/* ID is needed to determine kthread name */
 	id = ida_alloc(&pool->worker_ida, GFP_KERNEL);
@@ -2207,7 +2212,7 @@ static struct worker *create_worker(struct worker_pool *pool)
 	worker_attach_to_pool(worker, pool);
 
 	/* start the newly created worker */
-	raw_spin_lock_irq(&pool->lock);
+	raw_spin_lock_irqsave(&pool->lock, flags);
 
 	worker->pool->nr_workers++;
 	worker_enter_idle(worker);
@@ -2220,7 +2225,7 @@ static struct worker *create_worker(struct worker_pool *pool)
 	 */
 	wake_up_process(worker->task);
 
-	raw_spin_unlock_irq(&pool->lock);
+	raw_spin_unlock_irqrestore(&pool->lock, flags);
 
 	return worker;
 
@@ -2727,15 +2732,16 @@ static int worker_thread(void *__worker)
 {
 	struct worker *worker = __worker;
 	struct worker_pool *pool = worker->pool;
+	unsigned long flags;
 
 	/* tell the scheduler that this is a workqueue worker */
 	set_pf_worker(true);
 woke_up:
-	raw_spin_lock_irq(&pool->lock);
+	raw_spin_lock_irqsave(&pool->lock, flags);
 
 	/* am I supposed to die? */
 	if (unlikely(worker->flags & WORKER_DIE)) {
-		raw_spin_unlock_irq(&pool->lock);
+		raw_spin_unlock_irqrestore(&pool->lock, flags);
 		set_pf_worker(false);
 
 		set_task_comm(worker->task, "kworker/dying");
@@ -2792,7 +2798,7 @@ static int worker_thread(void *__worker)
 	 */
 	worker_enter_idle(worker);
 	__set_current_state(TASK_IDLE);
-	raw_spin_unlock_irq(&pool->lock);
+	raw_spin_unlock_irqrestore(&pool->lock, flags);
 	schedule();
 	goto woke_up;
 }