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

Ming Lei - 27.09.17, 16:27:

On Wed, Sep 27, 2017 at 09:57:37AM +0200, Martin Steigerwald wrote:

quoted

Hi Ming.

Ming Lei - 27.09.17, 13:48:

quoted

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

quoted

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 <redacted>

for V5.

Thanks for your test!

Two days and almost 6 hours, no hang yet. I bet the whole thing works. 
(3e45474d7df3bfdabe4801b5638d197df9810a79)

Tested-By: Martin Steigerwald <redacted>

(It could still hang after three days, but usually I got the first hang within 
the first two days.)

Thanks,
-- 
Martin