> + /* > + * 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? > @@ -2964,6 +2981,8 @@ void scsi_device_resume(struct scsi_device *sdev) > scsi_device_set_state(sdev, SDEV_RUNNING) == 0) > scsi_run_queue(sdev->request_queue); > mutex_unlock(&sdev->state_mutex); > + > + blk_set_preempt_only(sdev->request_queue, false); Same here.