linux-kernel - Re: [RFC/PATCH] debug workqueue deadlocks with lockdep

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Message-ID: <20070703194229.GB493@elte.hu>
Date:	Tue, 3 Jul 2007 21:42:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Johannes Berg <johannes@...solutions.net>,
	Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Sattler <tsattler@....de>
Subject: Re: [RFC/PATCH] debug workqueue deadlocks with lockdep


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

> Now we have a false positive if some time we queue B into that 
> workqueue, and this is not good.
> 
> We can avoid this problem if we put lockdep_map into work_struct, so 
> that wait_on_work() "locks" work->lockdep_map, while flush_workqueue() 
> takes wq->lockdep_map.
> 
> But probably we don't need this right now, at least until we really 
> have a lot of false positives while converting from flush_workqueue() 
> to cancel_work_sync/cancel_delayed_work_sync.

would be nice to map the real dependencies. Adding another lockdep_map 
is really low-cost and the lack of false positives is reassuring.

	Ingo
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