Date:	Mon, 24 Jun 2013 13:04:02 +0200
From:	Jan Kara <jack@...e.cz>
To:	Akira Fujita <a-fujita@...jp.nec.com>
Cc:	Jan Kara <jack@...e.cz>, Dmitry Monakhov <dmonakhov@...nvz.org>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [BUG] xfstest269 causes deadlock on linux-3.9.0 (ext4)

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.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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