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

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Message-ID: <20120103223505.GI31746@google.com>
Date:	Tue, 3 Jan 2012 14:35:05 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Hugh Dickins <hughd@...gle.com>, Shaohua Li <shaohua.li@...el.com>,
	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,
	x86@...nel.org
Subject: Re: [PATCH block/for-3.3/core] block: an exiting task should be
 allowed to create io_context

On Tue, Jan 03, 2012 at 02:13:01PM -0800, Tejun Heo wrote:
> > That's pretty odd. Given Hughs report as well, it sure does sound like
> > we now have some life time issues with cfqq's.
> 
> Hmmm... I disabled cfqq merge logic (commented out
> cfq_close_cooperator() and the following cfq_setup_merge() calls) in
> cfq_select_queue() and neither is triggering for quite a while now.
> Maybe cfqq refcnt is getting borked over cfqq merging / splitting?  It
> would also explain the low frequency of the issue too.  I'll try to
> further isolate it but It would be awesome if someone more familiar
> with the logic can go over that part.

Scrap that.  It triggered and yeah cfq_get_next_queue() is retrieving
empty cfqq from the service tree.

Thanks.

-- 
tejun
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