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

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Date:	Wed, 02 Nov 2011 21:37:06 +0900
From:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
CC:	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>,
	Mike Snitzer <snitzer@...hat.com>, gmuelas@...ibm.com
Subject: Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue
 resources at blk_release_queue())

On 10/31/11 22:00, Heiko Carstens wrote:
> On Mon, Oct 31, 2011 at 08:46:06PM +0900, Jun'ichi Nomura wrote:
>> Hm, dm_softirq_done is generic completion code of original
>> request in dm-multipath.
>> So oops here might be another manifestation of use-after-free.
>>
>> Do you always hit the oops at the same address?
> 
> I think we saw this bug the first time. But before that the scsi
> logging level was higher. Gonzalo is trying to recreate it with
> the same (old) scsi logging level.
> Afterwards we will try with barrier=0.
> 
> Both on v3.0.7 btw.
> 
>> Could you find corresponding source code line for
>> the crashed address, dm_softirq_done+0x72/0x140,
>> and which pointer was invalid?
> 
> It crashes in the inlined function dm_done() when trying to
> dereference tio (aka clone->end_io_data):
> 
> static void dm_done(struct request *clone, int error, bool mapped)
> {
>         int r = error;
>         struct dm_rq_target_io *tio = clone->end_io_data;
>         dm_request_endio_fn rq_end_io = tio->ti->type->rq_end_io;

Thank you. But, hmm. I have no idea about scenario.

struct dm_rq_target_io is a container of clone request
and clone->end_io_data points to its container.

  struct dm_rq_target_io {
        struct mapped_device *md;
        struct dm_target *ti;
        struct request *orig, clone;
        int error;
        union map_info info;
  };

If clone can be dereferenced, clone->end_io_data should be, too.

-- 
Jun'ichi Nomura, NEC Corporation
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