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

[Ming Lei <ming.lei@redhat.com>]

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


> 
> After an uptime of almost 6 days I am pretty confident that the V5 one fixes the 
> issue for me. So
> 
> Tested-by: Martin Steigerwald <martin@lichtvoll.de>
> 
> for V5.

Thanks for your test!


-- 
Ming