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Date:	Tue, 25 Jun 2013 19:06:53 +0900
From:	Akira Fujita <a-fujita@...jp.nec.com>
To:	Jan Kara <jack@...e.cz>
CC:	Dmitry Monakhov <dmonakhov@...nvz.org>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [BUG] xfstest269 causes deadlock on linux-3.9.0 (ext4)



(2013/06/24 20:04), Jan Kara wrote:
> On Tue 28-05-13 17:36:09, Akira Fujita wrote:
>> Hello,
>>
>> (2013/05/27 17:33), Jan Kara wrote:
>>> On Mon 27-05-13 12:16:01, Dmitry Monakhov wrote:
>>>> On Mon, 27 May 2013 10:49:11 +0900, Akira Fujita <a-fujita@...jp.nec.com> wrote:
>>>>> Hi Jan,
>>>>>
>>>>> (2013/05/15 11:57), Akira Fujita wrote:
>>>>>> Hi,
>>>>>>
>>>>>> (2013/05/15 6:37), Jan Kara wrote:
>>>>>>>       Hello,
>>>>>>>
>>>>>>> On Mon 13-05-13 15:49:24, Akira Fujita wrote:
>>>>>>>> I ran into the deaclock with xfs_test 269 on linux-3.9.0.
>>>>>>>> It seems happen between jbd2_log_wait_commit, sleep_on_buffer
>>>>>>>> and writeback_indoes (Please see ps log below).
>>>>>>>> Once it occurs we can't touch FS anymore.
>>>>>>>> In my case 300 - 1000 trials to occur. Is this known issue?
>>>>>>>>
>>>>>>>> The following kernels seems to have same problem:
>>>>>>>> - linux-3.5-rc5
>>>>>>>> - linux-3.8.5
>>>>>>>> - linux-3.9-rc7
>>>>>>>> And now I'm trying it on linux-3.10-rc1.
>>>>>>>>
>>>>>>>> # ./check generic/269
>>>>>>>> FSTYP         -- ext4
>>>>>>>> PLATFORM      -- Linux/x86_64 mcds1 3.9.0
>>>>>>>> MKFS_OPTIONS  -- /dev/sda12
>>>>>>>> MOUNT_OPTIONS -- -o acl,user_xattr /dev/sda12 /mnt/mp2
>>>>>>>>
>>>>>>>>
>>>>>>>> # ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:16,comm
>>>>>>>>       PID   TID CLS RTPRIO  NI PRI PSR %CPU STAT WCHAN            COMMAND
>>>>>>>>         1     1 TS       -   0  19   0  0.0 Ss   poll_schedule_ti init
>>>>>>>>         2     2 TS       -   0  19   0  0.0 S    kthreadd         kthreadd
>>>>>>>>         3     3 TS       -   0  19   0  0.0 S    smpboot_thread_f ksoftirqd/0
>>>>>>>> ...
>>>>>>>>      2391  2391 TS       -   0  19   2  0.1 D    jbd2_log_wait_co flush-8:0
>>>>>>>> ...
>>>>>>>> 22647 22647 TS       -   0  19   3  0.0 S    worker_thread    kworker/3:1
>>>>>>>> 22655 22655 TS       -   0  19   0  0.0 S    hrtimer_nanoslee sleep
>>>>>>>> 22657 22657 TS       -   0  19   2  0.0 R+   -                ps
>>>>>>>> 25330 25330 TS       -   0  19   0  0.0 S    worker_thread    kworker/0:0
>>>>>>>> 28963 28963 TS       -   0  19   1  0.0 S+   wait             loop_xfstests.s
>>>>>>>> 28964 28964 TS       -   0  19   1  0.0 S+   wait             check
>>>>>>>> 29180 29180 TS       -   0  19   3  0.0 S    kjournald2       jbd2/sda11-8
>>>>>>>> 29181 29181 TS       - -20  39   3  0.0 S<   rescuer_thread   ext4-dio-unwrit
>>>>>>>> 29199 29199 TS       -   0  19   3  0.0 S+   wait             269
>>>>>>>> 29391 29391 TS       -   0  19   0  0.6 D    sleep_on_buffer  jbd2/sda12-8
>>>>>>>> 29392 29392 TS       - -20  39   3  0.0 S<   rescuer_thread   ext4-dio-unwrit
>>>>>>>> 29394 29394 TS       -   0  19   0  0.0 S    wait             fsstress
>>>>>>>> 29505 29505 TS       -   0  19   3  0.0 D    writeback_inodes fsstress
>>>>>>>>
>>>>>>>> # df -T /dev/sda11 /dev/sda12
>>>>>>>> Filesystem    Type   1K-blocks      Used Available Use% Mounted on
>>>>>>>> /dev/sda11    ext4     9857264     22308   9327564   1% /mnt/mp1
>>>>>>>> /dev/sda12    ext4      499656    499656         0 100% /mnt/mp2
>>>>>>>       Thanks for report. No I don't think this problem has been reported
>>>>>>> before. Seeing that sda12 is out of space and fsstress hangs in
>>>>>>> writeback_inodes(), I suspect we have some deadlock in ENOSPC recovery path
>>>>>>> when we want to flush data to disk to reduce delalloc uncertainty. Can you
>>>>>>> run 'echo w >/proc/sysrq-trigger' when the deadlock happens and post your
>>>>>>> dmesg here? Thanks!
>>>>>>>
>>>>>>
>>>>>> Thanks for reply.
>>>>>> I'll take that information when the deadlock happens again.
>>>>>
>>>>> Finally, I got the following messages on linux-3.9.0.
>>>>> Could you take a look?
>>>> Is it a real deadlock?
>>>> umount wait for flush-8:0
>>>> flush wait for jbd2
>>>> jbd2 wait for bh.
>>>> All buffer-heads will be written at sooner or later.
>>>> It probably will require significant amount of time, because fs is too
>>>> fragmented(that is what this test all about), but it is not a deadlock.
>>>     Yeah, that is my analysis as well. I was only thinking whether we
>>> couldn't forget some buffer locked on some error recovery path (we are
>>> getting ENOSPC) but it's not obvious where it would be. Akira-san, could
>>> you also send us disassembly of your jbd2_journal_commit_transaction()
>>> function so that we can check where exactly offset 0xee0 is in the
>>> function?
>>>
>>> 								Honza
>>
>> I attached disasemble code of jbd2_journal_commit_tnrasaction,
>> please check it.
>    Thanks. I've looked into the disassembly now and we are waiting for the
> write of commit record to finish. We have submitted the buffer just before
> so it can hardly be some issue like forgotten locked buffer. Really
> strange. It looks like some problem in block layer, device driver, or HW
> itself... I'm thinking how to debug this further - it would be good if we
> had blktrace data just before the moment when the hang happens but given
> how hard this is to reproduce the traces would be extremly large...
> 
> One idea - can you try whether the problem reproduces with 'nobarrier'
> mount option? It could be some problem with flush / fua handling.
> 

OK, I'll try to reproduce this issue with 'nobarrier'
(and take blktrace log if I can).

Thanks,
Akira Fujita
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