linux-kernel - Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue resources at blk_release

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Date:	Mon, 7 Nov 2011 17:43:51 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Steffen Maier <maier@...ux.vnet.ibm.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>,
	"Taraka R. Bodireddy" <tarak.reddy@...ibm.com>,
	"Seshagiri N. Ippili" <seshagiri.ippili@...ibm.com>,
	"Manvanthara B. Puttashankar" <mputtash@...ibm.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Shaohua Li <shaohua.li@...el.com>, gmuelas@...ibm.com
Subject: Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue
 resources at blk_release_queue())

On Mon, Nov 07, 2011 at 10:36:49AM -0500, Mike Snitzer wrote:
> > struct pgpath is freed before dm_target when tearing down dm table.
> > So if the problematic completion was being done after freeing pgpath
> > but before freeing dm_target, crash would look like that
> > and what's happening seems the same for these dm crashes:
> > dm table was somehow destroyed while I/O was in-flight.
> 
> Could be the block layer's onstack plugging changes are at the heart of
> this.
> 
> I voiced onstack plugging concerns relative to DM some time ago
> (https://lkml.org/lkml/2011/3/9/450) but somehow convinced myself DM was
> fine to no longer need dm_table_unplug_all() etc.  Unfortunately I
> cannot recall _why_ I felt that was the case.
> 
> So DM needs further review relative to block's onstack plugging changes
> and DM IO completion.
> 
> > It's interesting that your test started to crash in dm with v3.0.7.
> > Have you gotten these dm crashes with v3.0.6 or before?
> > Have you hit the initially-reported scsi oops with v3.0.7?
> > Are your v3.0.6 and v3.0.7 compiled with same config and the tests
> > ran on same system?
> 
> If all 3.0.x fail: it would be interesting to know if 2.6.39 (which
> introduced the onstack plugging) also has these problems.

At least 2.6.39.1 failed as well, as reported already in June. At least
the crash looked similar back then:

http://marc.info/?l=linux-scsi&m=130824013229933&w=2

> Testing with
> 2.6.38 would be very insightful because it obviously doesn't have any of
> the onstack plugging churn.

Ok, we might try 2.6.38.8 (latest stable) and see what happens.
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