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

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Message-ID: <20081201234529.GA14025@linux.vnet.ibm.com>
Date:	Mon, 1 Dec 2008 15:45:29 -0800
From:	Mike Anderson <andmike@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	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

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,

-andmike
--
Michael Anderson
andmike@...ux.vnet.ibm.com
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