On Mon, Oct 02, 2017 at 06:52:25AM -0700, Christoph Hellwig wrote: > > + /* > > + * Simply quiesing SCSI device isn't safe, it is easy > > + * to use up requests because all these allocated requests > > + * can't be dispatched when device is put in QIUESCE. > > + * Then no request can be allocated and we may hang > > + * somewhere, such as system suspend/resume. > > + * > > + * So we set block queue in preempt only first, no new > > + * normal request can enter queue any more, and all pending > > + * requests are drained once blk_set_preempt_only() > > + * returns. Only RQF_PREEMPT is allowed in preempt only mode. > > + */ > > + blk_set_preempt_only(sdev->request_queue, true); > > + > > mutex_lock(&sdev->state_mutex); > > err = scsi_device_set_state(sdev, SDEV_QUIESCE); > > Why is this not under state_mutex so that we guarantee it's atomic > vs sdev state changes? It isn't necessary since what we want is to make sure only RQF_PREEMPT is allowed once blk_set_preempt_only() returns, and putting a lock before freezing queue might risk to deadlock. -- Ming