linux-kernel - Re: [PATCH block/for-3.3/core] block: an exiting task should be allowed to create io

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Date:	Sun, 25 Dec 2011 14:29:34 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Tejun Heo <tj@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	Hugh Dickins <hughd@...gle.com>, x86@...nel.org
Subject: Re: [PATCH block/for-3.3/core] block: an exiting task should be allowed
 to create io_context

On 2011-12-25 02:02, Tejun Heo wrote:
> While fixing io_context creation / task exit race condition,
> 6e736be7f2 "block: make ioc get/put interface more conventional and
> fix race on alloction" also prevented an exiting (%PF_EXITING) task
> from creating its own io_context.  This is incorrect as exit path may
> issue IOs, e.g. from exit_files(), and if those IOs are the first ones
> issued by the task, io_context needs to be created to process the IOs.
> 
> Combined with the existing problem of io_context / io_cq creation
> failure having the possibility of stalling IO, this problem results in
> deterministic full IO lockup with certain workloads.
> 
> Fix it by allowing io_context creation regardless of %PF_EXITING for
> %current.

Thanks, applied.

-- 
Jens Axboe

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