From mboxrd@z Thu Jan  1 00:00:00 1970
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue
 resources at blk_release_queue())
Date: Wed, 2 Nov 2011 14:47:30 +0100
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To: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>, Steffen Maier <maier@linux.vnet.ibm.com>, "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>, Hannes Reinecke <hare@suse.de>, Linux Kernel <linux-kernel@vger.kernel.org>, Alan Stern <stern@rowland.harvard.edu>, Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>, "Taraka R. Bodireddy" <tarak.reddy@in.ibm.com>, "Seshagiri N. Ippili" <seshagiri.ippili@in.ibm.com>, "Manvanthara B. Puttashankar" <mputtash@in.ibm.com>, Jeff Moyer <jmoyer@redhat.com>, Shaohua Li <shaohua.li@intel.com>, Mike Snitzer <snitzer@redhat.com>, gmuelas@de.ibm.com

On Wed, Nov 02, 2011 at 09:37:06PM +0900, Jun'ichi Nomura wrote:
> 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.

If it helps: the above *ti pointer is the only one that points to
an (invalid) vmalloc area address. Invalid means the page was unmapped
because it was freed because of DEBUG_PAGEALLOC.
All other addresses I followed to get to this one belong to
the 1:1 mapping of the kernel, so no vmalloc involved.