linux-kernel - Re: [BUG REPORT] Kernel panic on 3.9.0-rc7-4-gbb33db7

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Date:	Thu, 18 Apr 2013 12:10:44 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Tejun Heo <tj@...nel.org>, Wanlong Gao <gaowanlong@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung@...il.com>,
	Alasdair G Kergon <agk@...hat.com>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	Neil Brown <neilb@...e.de>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG REPORT] Kernel panic on 3.9.0-rc7-4-gbb33db7

On Thu, Apr 18, 2013 at 11:13 AM, Jens Axboe <axboe@...nel.dk> wrote:
> On Thu, Apr 18 2013, Tejun Heo wrote:
>> On Thu, Apr 18, 2013 at 10:39:00AM -0700, Jens Axboe wrote:
>> >
>> > Yep, thanks Linus for that hint... Must be someone abusing it for a
>> > flag field post submission? Crazy.
>>
>> Let's hope that's not the case because there'll be blood if it is. :)
>
> Yeah, it's beyond the amount of crazy I've come to expect from various
> random users of IO interfaces :-)

I think it's more likely to be some use-after-free after a long timeout.

Wanlong says it happens a few minutes after boot, so maybe something
times out a command, does the blk_complete_request(), and free's the
bio, which gets re-used before the softirq actually ends up running.

I note that Wanlong uses the SLAB allocator, not the SLUB one. I
wonder if the thing goes away with SLUB, and if not, if
CONFIG_SLUB_DEBUG_ON=y might help debug it?

                     Linus
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