Re: [Regression/XFS/PM] Freeze tasks failed in xfsaild

[Yu Chen]

Hi Dave,
On Tue, Nov 14, 2017 at 09:52:16AM +1100, Dave Chinner wrote:
> On Mon, Nov 13, 2017 at 06:31:39PM +0800, Yu Chen wrote:
> > Hi all,
> > Currently we are running hibernation stress test on a server
> > and unfortunately after 48 rounds of cycling, it fails at a
> > early stage that, the xfs task refuses to be frozen by the system:
> > 
> > [ 1934.221653] PM: Syncing filesystems ...
> > [ 1934.661517] PM: done.
> > [ 1934.664067] Freezing user space processes ... (elapsed 0.003 seconds) done.
> > [ 1934.675251] OOM killer disabled.
> > [ 1934.724317] PM: Preallocating image memory... done (allocated 6906555 pages)
> > [ 1954.666378] PM: Allocated 27626220 kbytes in 19.93 seconds (1386.16 MB/s)
> > [ 1954.673939] Freezing remaining freezable tasks ...
> > [ 1974.681089] Freezing of tasks failed after 20.001 seconds (1 tasks refusing to freeze, wq_busy=0):
> > [ 1974.691169] xfsaild/dm-1    D    0  1362      2 0x00000080
> > [ 1974.697283] Call Trace:
> > [ 1974.700014]  __schedule+0x3be/0x830
> > [ 1974.703898]  schedule+0x36/0x80
> > [ 1974.707440]  _xfs_log_force+0x143/0x280 [xfs]
> > [ 1974.712295]  ? schedule_timeout+0x16b/0x350
> > [ 1974.716953]  ? wake_up_q+0x80/0x80
> > [ 1974.720752]  ? xfsaild+0x16f/0x770 [xfs]
> > [ 1974.725134]  xfs_log_force+0x2c/0x80 [xfs]
> > [ 1974.729707]  xfsaild+0x16f/0x770 [xfs]
> > [ 1974.733885]  kthread+0x109/0x140
> > [ 1974.737480]  ? kthread+0x109/0x140
> > [ 1974.741271]  ? xfs_trans_ail_cursor_first+0x90/0x90 [xfs]
> > [ 1974.747284]  ? kthread_park+0x60/0x60
> > [ 1974.751354]  ret_from_fork+0x25/0x30
> > [ 1974.755366] Restarting kernel threads ... done.
> > [ 1978.259907] OOM killer enabled.
> > [ 1978.263405] Restarting tasks ... done.
> > 
> > The reason for this failure might be that,
> > while the kernel thread xfsaild/dm-1 is waiting for
> > xfs-buf/dm-1 to wake it up, however the latter
> > has already been frozen, thus xfsaild/dm-1 never
> > has a chance to be woken up and get froze. (Although
> > the xfsaild/dm-1 remains in TASK_UNINTERRUPTIBLE, which
> > is quite similar to 'frozen'.)
> 
> Should be fixed by this commit in the for-next branch:
> 
> 0bd89676c4fe xfs: check kthread_should_stop() after the setting of task state
> 
> That should get merged into 4.15 with the next merge...
>
I did not quite catch why above commit would fix the issue here,
according to
https://git.kernel.org/pub/scm/fs/xfs/xfs-linux.git/commit/?h=for-next&id=0bd89676c4fed53b003025bc4a5200861ac5d8ef
it tries to address a race condition between umount and xfsaild on
checking the kthread_should_stop() in order not to make
xfsaild falling asleep indefinitely.
But in our case, the xfsaild is waiting for the xfs-buf to wake
it up, and is nothing related to the kthread_should_stop() checking
here, did I miss something?
Thanks,
	Yu