linux-kernel - Re: [PATCH wq/for-4.5-fixes] workqueue: skip flush dependency checks for legacy workqueues

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Message-ID: <20160129183203.GQ3628@mtj.duckdns.org>
Date:	Fri, 29 Jan 2016 13:32:03 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, kernel-team@...com,
	Jon Hunter <jonathanh@...dia.com>, linux-tegra@...r.kernel.org
Subject: Re: [PATCH wq/for-4.5-fixes] workqueue: skip flush dependency checks
 for legacy workqueues

On Fri, Jan 29, 2016 at 05:59:46AM -0500, Tejun Heo wrote:
> fca839c00a12 ("workqueue: warn if memory reclaim tries to flush
> !WQ_MEM_RECLAIM workqueue") implemented flush dependency warning which
> triggers if a PF_MEMALLOC task or WQ_MEM_RECLAIM workqueue tries to
> flush a !WQ_MEM_RECLAIM workquee.
> 
> This assumes that workqueues marked with WQ_MEM_RECLAIM sit in memory
> reclaim path and making it depend on something which may need more
> memory to make forward progress can lead to deadlocks.  Unfortunately,
> workqueues created with the legacy create*_workqueue() interface
> always have WQ_MEM_RECLAIM regardless of whether they are depended
> upon memory reclaim or not.  These spurious WQ_MEM_RECLAIM markings
> cause spurious triggering of the flush dependency checks.
...

Applied to wq/for-4.5-fixes.

Thanks.

-- 
tejun