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 -- Ming
