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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: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Oleg 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Lai Jiangshan 2009-04-02 16:58:24 -07:00 committed by Linus Torvalds
parent 1ee1184485
commit 2355b70fd5
1 changed files with 11 additions and 30 deletions
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41
kernel/workqueue.c
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@ -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);
}
@ -368,29 +358,20 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
{
int active;
int active = 0;
struct wq_barrier barr;
if (cwq->thread == current) {
/*
* Probably keventd trying to flush its own queue. So simply run
* it by hand rather than deadlocking.
*/
run_workqueue(cwq);
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);
active = 1;
} else {
struct wq_barrier barr;
active = 0;
spin_lock_irq(&cwq->lock);
if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
insert_wq_barrier(cwq, &barr, &cwq->worklist);
active = 1;
}
spin_unlock_irq(&cwq->lock);
if (active)
wait_for_completion(&barr.done);
}
spin_unlock_irq(&cwq->lock);
if (active)
wait_for_completion(&barr.done);
return active;
}