linux-kernel - Re: [PATCH 2.6.28-rc6] block: internal dequeue shouldn't start timer

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Date:	Wed, 3 Dec 2008 12:36:36 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Mike Anderson <andmike@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH 2.6.28-rc6] block: internal dequeue shouldn't start timer

On Mon, Dec 01 2008, Mike Anderson wrote:
> Tejun Heo <tj@...nel.org> wrote:
> > blkdev_dequeue_request() and elv_dequeue_request() are equivalent and
> > both start the timeout timer.  Barrier code dequeues the original
> > barrier request but doesn't passes the request itself to lower level
> > driver, only broken down proxy requests; however, as the original
> > barrier code goes through the same dequeue path and timeout timer is
> > started on it.  If barrier sequence takes long enough, this timer
> > expires but the low level driver has no idea about this request and
> > oops follows.
> > 
> > Timeout timer shouldn't have been started on the original barrier
> > request as it never goes through actual IO.  This patch unexports
> > elv_dequeue_request(), which has no external user anyway, and makes it
> > operate on elevator proper w/o adding the timer and make
> > blkdev_dequeue_request() call elv_dequeue_request() and add timer.
> > Internal users which don't pass the request to driver - barrier code
> > and end_that_request_last() - are converted to use
> > elv_dequeue_request().
> > 
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > Cc: Mike Anderson <andmike@...ux.vnet.ibm.com>
> > ---
> > Mike, this should fix the problem you were seeing (blk_add_timer on
> > requests w/o REQ_STARTED set).
> > 
> 
> Yes this fixed the "w/o REQ_STARTED" error I was seeing on a distro kernel
> and a mainline system. 

Thanks Tejun, this makes sense. I'll make sure it goes upstream asap.

-- 
Jens Axboe

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