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, 9 insertions, 5 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index cd863511dedb..13bb54f26736 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -504,6 +504,12 @@ struct request_queue {
          * various queue flags, see QUEUE_* below
          */
         unsigned long           queue_flags;
+        /*
+         * Number of contexts that have called blk_set_pm_only(). If this
+         * counter is above zero then only RQF_PM and RQF_PREEMPT requests are
+         * processed.
+         */
+        atomic_t                pm_only;
 
         /*
          * ida allocated id for this queue.  Used to index queues from
@@ -698,7 +704,6 @@ struct request_queue {
 #define QUEUE_FLAG_REGISTERED  26       /* queue has been registered to a disk */
 #define QUEUE_FLAG_SCSI_PASSTHROUGH 27  /* queue supports SCSI commands */
 #define QUEUE_FLAG_QUIESCED    28       /* queue has been quiesced */
-#define QUEUE_FLAG_PREEMPT_ONLY 29      /* only process REQ_PREEMPT requests */
 
 #define QUEUE_FLAG_DEFAULT      ((1 << QUEUE_FLAG_IO_STAT) |            \
                                  (1 << QUEUE_FLAG_SAME_COMP)    |       \
@@ -736,12 +741,11 @@ bool blk_queue_flag_test_and_clear(unsigned int flag, struct request_queue *q);
         ((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
                              REQ_FAILFAST_DRIVER))
 #define blk_queue_quiesced(q)   test_bit(QUEUE_FLAG_QUIESCED, &(q)->queue_flags)
-#define blk_queue_preempt_only(q)                               \
-        test_bit(QUEUE_FLAG_PREEMPT_ONLY, &(q)->queue_flags)
+#define blk_queue_pm_only(q)    atomic_read(&(q)->pm_only)
 #define blk_queue_fua(q)        test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags)
 
-extern int blk_set_preempt_only(struct request_queue *q);
-extern void blk_clear_preempt_only(struct request_queue *q);
+extern void blk_set_pm_only(struct request_queue *q);
+extern void blk_clear_pm_only(struct request_queue *q);
 
 static inline int queue_in_flight(struct request_queue *q)
 {