Re: Crash in rbd, need advice

[Hannes Landeholm]

On Fri, Apr 4, 2014 at 1:08 PM, Ilya Dryomov <ilya.dryomov@xxxxxxxxxxx> wrote:
> On Wed, Apr 2, 2014 at 12:18 AM, Hannes Landeholm <hannes@xxxxxxxxxxxxxx> 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.

If we continue to get kernel panics we should at least be able to
provide a proper stack trace in the future.

Thank you for your time,
Hannes
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