linux-kernel - Re: Changes to Linux/SCSI target mode infrastructure for v2.6.28

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Message-Id: <1228206646.6229.46.camel@haakon2.linux-iscsi.org>
Date:	Tue, 02 Dec 2008 00:30:46 -0800
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Mike Anderson <andmike@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	Christoph Hellwig <hch@....de>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Andrew Morton <akpm@...l.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Hannes Reinecke <hare@...e.de>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Linux-iSCSI.org Target Dev" 
	<linux-iscsi-target-dev@...glegroups.com>
Subject: Re: Changes to Linux/SCSI target mode infrastructure for v2.6.28

On Mon, 2008-12-01 at 22:40 -0800, Mike Anderson wrote:
> Nicholas A. Bellinger <nab@...ux-iscsi.org> wrote:
> > On Tue, 2008-12-02 at 13:18 +0900, Tejun Heo wrote:
> > > 
> > > >>> The other one is a BUG_ON in blk/blk-timeout.c:177 in blk_add_timeout()
> > > >>> that happens after a few hundred MB of READ_10 traffic, which also
> > > >>> appears to pass through elv_dequeue_request() at some point:
> > > >>>
> > > >>> http://linux-iscsi.org/builds/user/nab/2.6.28-rc6-oops-2.png
> > > >>> http://linux-iscsi.org/builds/user/nab/2.6.28-rc6-oops-4.png
> > >
> > > Hmmm... this means blk_add_timer() is being called after the request
> > > is already completed.
> 
> or is it possible since elv_dequeue_request BUG_ON check of queuelist did
> not trigger a request is on the queuelist with a timeout_list not empty.
> 
> It would be interesting for a debug run to change the
> "BUG_ON(!list_empty(&req->timeout_list))" in blk_add_timer to print out
> the cmd_flags plus req->atomic_flags and also add a
> "BUG_ON(!list_empty(&rq->timeout_list))" to elv_insert to ensure a request
> is never added to the queuelist with a timeout_list not empty.
> 

Ok, so blk_dump_rq_flags() is now being called in
block/blk-timeout.c:blk_add_timer() for the case
BUG_ON(list_empty(&req->timeout_list)) case:

http://linux-iscsi.org/builds/user/nab/2.6.28-rc6-oops-6.png

Hmm, the outputted "sector " range is definately is bogus, as the only
READ_10 that have been sent are at LBA offset 0 for 8 * 512 byte sectors
for the partition table during Open/iSCSI LUN scanning.

--nab


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