block, scsi: Change the preempt-only flag into a counter

The RQF_PREEMPT flag is used for three purposes:
- In the SCSI core, for making sure that power management requests
  are executed even if a device is in the "quiesced" state.
- For domain validation by SCSI drivers that use the parallel port.
- In the IDE driver, for IDE preempt requests.
Rename "preempt-only" into "pm-only" because the primary purpose of
this mode is power management. Since the power management core may
but does not have to resume a runtime suspended device before
performing system-wide suspend and since a later patch will set
"pm-only" mode as long as a block device is runtime suspended, make
it possible to set "pm-only" mode from more than one context. Since
with this change scsi_device_quiesce() is no longer idempotent, make
that function return early if it is called for a quiesced queue.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Cc: Jianchao Wang <jianchao.w.wang@oracle.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index eb97d2dd3651..62348412ed1b 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -3046,11 +3046,14 @@ scsi_device_quiesce(struct scsi_device *sdev)
 	 */
 	WARN_ON_ONCE(sdev->quiesced_by && sdev->quiesced_by != current);
 
-	blk_set_preempt_only(q);
+	if (sdev->quiesced_by == current)
+		return 0;
+
+	blk_set_pm_only(q);
 
 	blk_mq_freeze_queue(q);
 	/*
-	 * Ensure that the effect of blk_set_preempt_only() will be visible
+	 * Ensure that the effect of blk_set_pm_only() will be visible
 	 * for percpu_ref_tryget() callers that occur after the queue
 	 * unfreeze even if the queue was already frozen before this function
 	 * was called. See also https://lwn.net/Articles/573497/.
@@ -3063,7 +3066,7 @@ scsi_device_quiesce(struct scsi_device *sdev)
 	if (err == 0)
 		sdev->quiesced_by = current;
 	else
-		blk_clear_preempt_only(q);
+		blk_clear_pm_only(q);
 	mutex_unlock(&sdev->state_mutex);
 
 	return err;
@@ -3088,7 +3091,7 @@ void scsi_device_resume(struct scsi_device *sdev)
 	mutex_lock(&sdev->state_mutex);
 	WARN_ON_ONCE(!sdev->quiesced_by);
 	sdev->quiesced_by = NULL;
-	blk_clear_preempt_only(sdev->request_queue);
+	blk_clear_pm_only(sdev->request_queue);
 	if (sdev->sdev_state == SDEV_QUIESCE)
 		scsi_device_set_state(sdev, SDEV_RUNNING);
 	mutex_unlock(&sdev->state_mutex);