Re: 100% system time hang with git f2fs

[Jaegeuk Kim <jaegeuk@kernel.org>]

On Fri, Oct 02, 2015 at 10:53:40AM +0200, Marc Lehmann wrote:
> On Thu, Oct 01, 2015 at 08:51:24PM +0200, Marc Lehmann <schmorp@schmorp.de> wrote:
> > Ok, for completeness, here is the full log and a description of what was
> > going on.
> 
> Ok, so I did a fsck, which took one hour, which is not very good, but I
> don't use fsck very often. It didn't find any problems (everything Ok).
> 
> However, I have a freeze. When I mount the volume, start a du on it, and after
> a while do:

How was your scenario?
Did you delete device before, or just plain mount and umount?

>    echo 3 >/proc/sys/vm/drop_caches
> 
> Then this process hangs with 100% sys time. /proc/../stack gives no usable
> backtrace.

This should be shrinker is stuck on mutex. I suspect a deadlock.
Can you do this, if you meet this again?

# echo l > /proc/sysrq-trigger
# echo w > /proc/sysrq-trigger
# demsg

Thanks,

> 
> umount on the f2fs volume also hangs:
> 
>    [<ffffffff8139ba03>] call_rwsem_down_write_failed+0x13/0x20
>    [<ffffffff8118086d>] unregister_shrinker+0x1d/0x70
>    [<ffffffff811e7911>] deactivate_locked_super+0x41/0x60
>    [<ffffffff811e7eee>] deactivate_super+0x4e/0x70
>    [<ffffffff81204733>] cleanup_mnt+0x43/0x90
>    [<ffffffff812047d2>] __cleanup_mnt+0x12/0x20
>    [<ffffffff8108e8a4>] task_work_run+0xc4/0xe0
>    [<ffffffff81012fa7>] do_notify_resume+0x97/0xb0
>    [<ffffffff8178896f>] int_signal+0x12/0x17
>    [<ffffffffffffffff>] 0xffffffffffffffff
> 
> -- 
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