Re: [PATCH v10 00/10] block, scsi, md: Improve suspend and resume

[Bart Van Assche <Bart.VanAssche@wdc.com>]

On Sat, 2017-10-21 at 17:59 +0000, Bart Van Assche wrote:
> On Sat, 2017-10-21 at 19:21 +0200, Oleksandr Natalenko wrote:
> > I've cherry-picked this series for current upstream/master branch, and got
> > this while performing another suspend try:
> > 
> > ===
> > [   62.415890] Freezing of tasks failed after 20.007 seconds (1 tasks refusing 
> > to freeze, wq_busy=0):
> > [   62.421150] xfsaild/dm-7    D    0   289      2 0x80000000
> > [   62.425800] Call Trace:
> > [   62.428902]  __schedule+0x239/0x870
> > [   62.431834]  schedule+0x33/0x90
> > [   62.434156]  _xfs_log_force+0x143/0x280 [xfs]
> > [   62.438767]  ? schedule_timeout+0x188/0x390
> > [   62.443592]  ? wake_up_q+0x80/0x80
> > [   62.446545]  ? xfsaild+0x18d/0x780 [xfs]
> > [   62.449702]  xfs_log_force+0x2c/0x90 [xfs]
> > [   62.453217]  xfsaild+0x18d/0x780 [xfs]
> > [   62.456717]  kthread+0x124/0x140
> > [   62.459237]  ? kthread+0x124/0x140
> > [   62.461818]  ? xfs_trans_ail_cursor_first+0x90/0x90 [xfs]
> > [   62.465146]  ? kthread_create_on_node+0x70/0x70
> > [   62.467331]  ret_from_fork+0x25/0x30
> > [   62.474386] Restarting kernel threads ... done.
> > ===
> 
> Thank you for having tested v10 of this patch series. This patch series only
> changes the behavior of suspending devices but not the behavior of freezing
> the XFS kernel threads. During suspend task freezing occurs *before*
> suspending devices. In other words, the lockup occurred before the code was
> reached that is modified by this patch series. So I think you ran into a bug
> in the XFS code and not into a bug in this patch series.

On second thought, I want to take back what I wrote about XFS. Since xfsaild()
can submit I/O, what may have happened is that the md kernel thread got frozen
before the XFS kernel thread. I will see what I can do to avoid freeze failures
like the one you reported.

Bart.