linux-kernel - Re: workqueue destruction BUG

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Date:	Tue, 24 Aug 2010 12:37:48 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Tejun Heo <tj@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: workqueue destruction BUG_ON

Hi,

> > In our testing with iwlwifi, we keep running into this BUG_ON:
> > 
> > 	BUG_ON(cwq->nr_active);
> > 
> > in destroy_workqueue(). This is quite unhelpful, and since the code
> > flushes the workqueue I really don't see how this could be happening,
> > unless maybe there's cross-talk between this and other workqueues?
> 
> Flushing the workqueue doesn't guarantee that the workqueue stays
> empty.

True.

> It just flushes the currently pending works.  If there are
> requeueing works or something else is queueing new works, workqueue
> won't be empty.  The check is new.  Previously, workqueue code didn't
> check whether the workqueue is actually empty.  Now that the worklist
> is shared, we need such check in place.  There was also a similar
> report on ath9k.  I think it's most likely that something is queueing
> works on a dying wokrqueue in the wireless common code.

I think in my iwlwifi case it's actually destroying the iwlwifi
workqueue (not sure why it even exists though).

>   I'll prep a
> debug patch to print out some details.

That'd be helpful, thanks!

johannes

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