linux-kernel - Re: [PATCH] workqueue: relax lockdep annotation on flush

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Date:	Mon, 03 Jan 2011 10:31:31 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ingo Molnar <mingo@...hat.com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: relax lockdep annotation on flush_work()

On Wed, 2010-12-29 at 13:57 +0100, Tejun Heo wrote:
> Currently, the lockdep annotation in flush_work() requires exclusive
> access on the workqueue the target work is queued on and triggers
> warning if a work is trying to flush another work on the same
> workqueue; however, this is no longer true as workqueues can now
> execute multiple works concurrently.
> 
> This patch adds lock_map_acquire_read() and make process_one_work()
> hold read access to the workqueue while executing a work and
> start_flush_work() check for write access if concurrnecy level is one
> and read access if higher.
> 
> This better represents what's going on and removes spurious lockdep
> warnings which are triggered by fake dependency chain created through
> flush_work().

Is this still true in the low memory situation where we're running the
emergency thread? I can imagine the emergency thread trying to flush
itself isn't really a good thing.
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