Bart, On Fri, Sep 08, 2017 at 04:52:21PM -0700, Bart Van Assche wrote: > Hello Jens, > > Recently it was reported on the block layer mailing list that suspend > does not work reliably neither for the legacy block layer nor for blk-mq. What is the issue? Why is it not reliably? Please describe it clearly. > The purpose of this patch series is to make device suspend work reliably > without affecting the hot path significantly and without introducing any > race conditions between request queue cleanup and blk_get_request(). If you mean the approach in my patchset, please say it clearly. I replied you already, but I am happy to reply you again. Looks you do not understand the root cause behind I/O hang during suspend/resume reported by Oleksandr. Let me explain it again: - the issue is not suspend/resume only, it is about SCSI quiesce vs. RQF_PREEMPT. - when SCSI device is put into quiesce, only RQF_PREEMPT request is allowed to dispatch to lld, and other requests can't be dispatched successfully. - so if requests pool are used up during SCSI quiesce, no request can be allocated for RQF_PREEMPT and these requests can't be freed too, so I/O hang is caused because the pool is often very limited, and easy to be consumed up Except for the suspend I/O hang reported by Oleksandr, we also have other I/O hang related with SCSI quiesce, both belongs to the same kind of issue. I don't see the issue above addressed by this patchset, so maybe you are trying to fix another PM specific issue(not reported by Oleksandr), I am just confused. So again, please describe the issue to be addressed clearly first! -- Ming
