Re: [RFC/PATCH] debug workqueue deadlocks with lockdep
From: Oleg Nesterov <hidden>
Date: 2007-06-30 11:46:20
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On 06/30, Ingo Molnar wrote:
On Thu, 2007-06-28 at 19:33 +0200, Johannes Berg wrote:quoted
No, that's not right either, but Arjan just helped me a bit with how lockdep works and I think I have the right idea now. Ignore this for now, I'll send a new patch in a few days.ok. But in general, this is a very nice idea! i've Cc:-ed Oleg. Oleg, what do you think? I think we should keep all the workqueue APIs specified in a form that makes them lockdep coverable like Johannes did. This debug mechanism could have helped with the recent DVB lockup that Thomas Sattler reported.
I think this idea is great! Johannes, could you change wait_on_work() as well? Most users of flush_workqueue() should be converted to use it.
quoted hunk ↗ jump to hunk
@@ -342,6 +351,9 @@ static int flush_cpu_workqueue(struct cp } else { struct wq_barrier barr; + lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_); + lock_release(&cwq->wq->lockdep_map, 0, _THIS_IP_); + active = 0; spin_lock_irq(&cwq->lock);
I am not sure why you skip "if (cwq->thread == current)" case, it can deadlock in the same way. But, perhaps we should not change flush_cpu_workqueue(). If we detect the deadlock, we will have num_online_cpus() reports, yes? And,
quoted hunk ↗ jump to hunk
if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {@@ -376,6 +388,8 @@ void fastcall flush_workqueue(struct wor int cpu; might_sleep(); + lock_acquire(&wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_); + lock_release(&wq->lockdep_map, 0, _THIS_IP_);
one of the 2 callers was already modified. Perhaps it is better to add lock_acquire() into the second caller, cleanup_workqueue_thread(), but skip flush_cpu_workqueue() ? Oleg.