Re: [PATCH V6 0/6] block/scsi: safe SCSI quiescing

Oleksandr Natalenko
2017-09-28T08:11:20Z

Hey.

I can confirm that v6 of your patchset still works well for me. Tested on
v4.13 kernel.

Thanks.

On středa 27. září 2017 10:52:41 CEST Ming Lei wrote:
> On Wed, Sep 27, 2017 at 04:27:51PM +0800, Ming Lei wrote:
> > On Wed, Sep 27, 2017 at 09:57:37AM +0200, Martin Steigerwald wrote:
> > > Hi Ming.
> > >
> > > Ming Lei - 27.09.17, 13:48:
> > > > Hi,
> > > >
> > > > The current SCSI quiesce isn't safe and easy to trigger I/O deadlock.
> > > >
> > > > Once SCSI device is put into QUIESCE, no new request except for
> > > > RQF_PREEMPT can be dispatched to SCSI successfully, and
> > > > scsi_device_quiesce() just simply waits for completion of I/Os
> > > > dispatched to SCSI stack. It isn't enough at all.
> > > >
> > > > Because new request still can be comming, but all the allocated
> > > > requests can't be dispatched successfully, so request pool can be
> > > > consumed up easily.
> > > >
> > > > Then request with RQF_PREEMPT can't be allocated and wait forever,
> > > > meantime scsi_device_resume() waits for completion of RQF_PREEMPT,
> > > > then system hangs forever, such as during system suspend or
> > > > sending SCSI domain alidation.
> > > >
> > > > Both IO hang inside system suspend[1] or SCSI domain validation
> > > > were reported before.
> > > >
> > > > This patch introduces preempt only mode, and solves the issue
> > > > by allowing RQF_PREEMP only during SCSI quiesce.
> > > >
> > > > Both SCSI and SCSI_MQ have this IO deadlock issue, this patch fixes
> > > > them all.
> > > >
> > > > V6:
> > > > - borrow Bart's idea of preempt only, with clean
> > > >
> > > > implementation(patch 5/patch 6)
> > > >
> > > > - needn't any external driver's dependency, such as MD's
> > > > change
> > >
> > > Do you want me to test with v6 of the patch set? If so, it would be nice
> > > if
> > > you´d make a v6 branch in your git repo.
> >
> > Hi Martin,
> >
> > I appreciate much if you may run V6 and provide your test result,
> > follows the branch:
> >
> > https://github.com/ming1/linux/tree/blk_safe_scsi_quiesce_V6
> >
> > https://github.com/ming1/linux.git #blk_safe_scsi_quiesce_V6
>
> Also follows the branch against V4.13:
>
> https://github.com/ming1/linux/tree/v4.13-safe-scsi-quiesce_V6_for_test
>
> https://github.com/ming1/linux.git #v4.13-safe-scsi-quiesce_V6_for_test