On 07/05, Johannes Berg wrote:
>
> @@ -257,7 +261,9 @@ static void run_workqueue(struct cpu_wor
>
> BUG_ON(get_wq_data(work) != cwq);
> work_clear_pending(work);
> + lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
> f(work);
> + lock_release(&cwq->wq->lockdep_map, 1, _THIS_IP_);
Johannes, my apologies. You were worried about recursion, and you were right,
sorry!
Currently it is allowed that work->func() does flush_workqueue() on its own
workqueue. So we have
run_workqueue()
work->func()
flush_workqueue()
run_workqueue()
All but work->func() take wq->lockdep_map, I guess check_deadlock() won't be
happy.
In your initial patch, wq->lockdep_map was taken in flush_cpu_workqueue() when
cwq->thread != current, but this is still not enough. Because we take the same
lock when flush_workqueue() does flush_cpu_workqueue() on another CPU.
run_workqueue() is easy, it can check cwq->run_depth == 1 before lock/unlock.
Anybody sees a simple soultion? Perhaps, some clever trick with LOCKDEP ?
OTOH. Perhaps we can can forbid such a behaviour? Andrew, do you know any
good example of "keventd trying to flush its own queue" ?
In any case, I think both patches are great, thanks for doing this!
Oleg.
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