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Commit 2355b70f authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Linus Torvalds
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workqueue: avoid recursion in run_workqueue() 



1) lockdep will complain when run_workqueue() performs recursion.

2) The recursive implementation of run_workqueue() means that
   flush_workqueue() and its documentation are inconsistent.  This may
   hide deadlocks and other bugs.

3) The recursion in run_workqueue() will poison cwq->current_work, but
   flush_work() and __cancel_work_timer(), etcetera need a reliable
   cwq->current_work.

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1ee11844

kernel/workqueue.c

+11 −30
Original line number Diff line number Diff line
@@ -48,8 +48,6 @@ struct cpu_workqueue_struct { 


	struct workqueue_struct *wq;

	struct task_struct *thread;



	int run_depth;		/* Detect run_workqueue() recursion depth */

} ____cacheline_aligned;



/*
@@ -262,13 +260,6 @@ EXPORT_SYMBOL_GPL(queue_delayed_work_on); 
static void run_workqueue(struct cpu_workqueue_struct *cwq)

{

	spin_lock_irq(&cwq->lock);

	cwq->run_depth++;

	if (cwq->run_depth > 3) {

		/* morton gets to eat his hat */

		printk("%s: recursion depth exceeded: %d\n",

			__func__, cwq->run_depth);

		dump_stack();

	}

	while (!list_empty(&cwq->worklist)) {

		struct work_struct *work = list_entry(cwq->worklist.next,

						struct work_struct, entry);
@@ -311,7 +302,6 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq) 
		spin_lock_irq(&cwq->lock);

		cwq->current_work = NULL;

	}

	cwq->run_depth--;

	spin_unlock_irq(&cwq->lock);

}
@@ -368,19 +358,11 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq, 


static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)

{

	int active;



	if (cwq->thread == current) {

		/*

		 * Probably keventd trying to flush its own queue. So simply run

		 * it by hand rather than deadlocking.

		 */

		run_workqueue(cwq);

		active = 1;

	} else {

	int active = 0;

	struct wq_barrier barr;



		active = 0;

	WARN_ON(cwq->thread == current);



	spin_lock_irq(&cwq->lock);

	if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {

		insert_wq_barrier(cwq, &barr, &cwq->worklist);
@@ -390,7 +372,6 @@ static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq) 


	if (active)

		wait_for_completion(&barr.done);

	}



	return active;

}