Date:	Fri, 4 Apr 2014 17:10:32 +0400
From:	Ilya Dryomov <ilya.dryomov@...tank.com>
To:	Hannes Landeholm <hannes@...pstarter.io>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ceph Development <ceph-devel@...r.kernel.org>,
	Sage Weil <sage@...tank.com>, Sage Weil <sage@...dream.net>,
	Alex Elder <elder@...tank.com>,
	Yehuda Sadeh <yehuda@...newdream.net>,
	Thorwald Lundqvist <thorwald@...pstarter.io>
Subject: Re: Crash in rbd, need advice

On Fri, Apr 4, 2014 at 4:25 PM, Hannes Landeholm <hannes@...pstarter.io> wrote:
> On Fri, Apr 4, 2014 at 1:08 PM, Ilya Dryomov <ilya.dryomov@...tank.com> wrote:
>> On Wed, Apr 2, 2014 at 12:18 AM, Hannes Landeholm <hannes@...pstarter.io> wrote:
>>> Hello,
>>>
>>> We're running a couple of Arch Linux servers of version 3.13.5-1 in
>>> production and suddenly one of them had a strange problem after
>>> running for a few days. One process (pid 319) was running with a few
>>> threads, one of those threads (pid 322) was eating 100% cpu. I assumed
>>> it was stuck in an infinite loop (this was our own software so I
>>> assumed we had a bug) so I sent a SIGKILL to 319 which caused all
>>> other threads to exit and it turning into a zombie, but thread 322 was
>>> still running. After trying to stop some other services and failing I
>>> realized that sending any signals to any process now didn't work at
>>> all in the system.
>>>
>>> This was the process stack output:
>>>
>>> $ cat /proc/319/stack
>>> [<ffffffff810642fa>] do_exit+0x73a/0xa80
>>> [<ffffffff810646bf>] do_group_exit+0x3f/0xa0
>>> [<ffffffff81073295>] get_signal_to_deliver+0x295/0x5f0
>>> [<ffffffff810144a8>] do_signal+0x48/0x950
>>> [<ffffffff81014e18>] do_notify_resume+0x68/0xa0
>>> [<ffffffff8152326a>] int_signal+0x12/0x17
>>> [<ffffffffffffffff>] 0xffffffffffffffff
>>> $ cat /proc/319/task/322/stack
>>> [<ffffffff8151c11a>] error_exit+0x2a/0x60
>>> [<ffffffffffffffff>] 0xffffffffffffffff
>>>
>>> We're using ceph + rbd and this happened right after doing a rbd
>>> mapping (mounting it) or during the mapping itself, so we suspected
>>> rbd.
>>>
>>> A few days later (today) we had a server crash in another server, same
>>> version+distro and it had also just been running a few days as well.
>>> After starting it again we found the following in the system log:
>>>
>>> hostname kernel: BUG: unable to handle kernel paging request at ffff87fff75ad450
>>> hostname kernel: IP: [<ffffffffa018c196>] rbd_img_request_fill+0x126/0x930 [rbd]
>>
>> Can you try gdb'ing that exact rbd.ko and
>>
>> (gdb) list *rbd_img_request_fill+0x126
>>
>> Also, the entire stack trace pertaining to rbd_img_request_fill would
>> help.
>>
>> Thanks,
>>
>>                 Ilya
>
> Sorry, rbd was not built with any symbols and there was no other
> output in the journal.
>
> We're building a debug version of Linux 3.14 (with symbols) now that
> is currently being tested and we hope that we can roll it out today. I
> saw that at least one commit (638c323 rbd: drop an unsafe assertion)
> looks like something that could fix a crash that has been happening
> regularly on one of our development servers:
> http://i.imgur.com/pEKsmql.jpg (rbd_img_obj_callback in the stack
> trace). It might be related to the production crash we had.

Yeah, it most probably is.  However, a bogus dereference in
rbd_img_request_fill is something I haven't seen before.  If you have
that rbd.ko lying around, send it along, just in case.

Thanks,

                Ilya
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