linux-kernel - Re: [PATCH 1/2] workqueue: debug flushing deadlocks with lockdep

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Message-ID: <20070705144047.GA9548@elte.hu>
Date:	Thu, 5 Jul 2007 16:40:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Johannes Berg <johannes@...solutions.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/2] workqueue: debug flushing deadlocks with lockdep


* Oleg Nesterov <oleg@...sign.ru> wrote:

> 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.

yep.

> OTOH. Perhaps we can can forbid such a behaviour? Andrew, do you know 
> any good example of "keventd trying to flush its own queue" ?

i'd prefer to make the API a little bit stricter: such recursion is 
nasty. Btw., what mechanism prevents the second instance of 
run_workqueue() calling into a work->func() again?

	Ingo
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