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@xxxxxxxxxxxx> > > for V5. Thanks for your test! -- Ming
