scsi: block: Fix a race in the runtime power management code

With the current implementation the following race can happen:

 * blk_pre_runtime_suspend() calls blk_freeze_queue_start() and
   blk_mq_unfreeze_queue().

 * blk_queue_enter() calls blk_queue_pm_only() and that function returns
   true.

 * blk_queue_enter() calls blk_pm_request_resume() and that function does
   not call pm_request_resume() because the queue runtime status is
   RPM_ACTIVE.

 * blk_pre_runtime_suspend() changes the queue status into RPM_SUSPENDING.

Fix this race by changing the queue runtime status into RPM_SUSPENDING
before switching q_usage_counter to atomic mode.

Link: https://lore.kernel.org/r/[email protected]
Fixes: 986d413 ("blk-mq: Enable support for runtime power management")
Cc: Ming Lei <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: stable <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>
Acked-by: Alan Stern <[email protected]>
Acked-by: Stanley Chu <[email protected]>
Co-developed-by: Can Guo <[email protected]>
Signed-off-by: Can Guo <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

block/blk-pm.c

@@ -67,6 +67,10 @@ int blk_pre_runtime_suspend(struct request_queue *q)
 
 	WARN_ON_ONCE(q->rpm_status != RPM_ACTIVE);
 
+	spin_lock_irq(&q->queue_lock);
+	q->rpm_status = RPM_SUSPENDING;
+	spin_unlock_irq(&q->queue_lock);
+
 	/*
 	 * Increase the pm_only counter before checking whether any
 	 * non-PM blk_queue_enter() calls are in progress to avoid that any
@@ -89,15 +93,14 @@ int blk_pre_runtime_suspend(struct request_queue *q)
 	/* Switch q_usage_counter back to per-cpu mode. */
 	blk_mq_unfreeze_queue(q);
 
-	spin_lock_irq(&q->queue_lock);
-	if (ret < 0)
+	if (ret < 0) {
+		spin_lock_irq(&q->queue_lock);
+		q->rpm_status = RPM_ACTIVE;
 		pm_runtime_mark_last_busy(q->dev);
-	else
-		q->rpm_status = RPM_SUSPENDING;
-	spin_unlock_irq(&q->queue_lock);
+		spin_unlock_irq(&q->queue_lock);
 
-	if (ret)
 		blk_clear_pm_only(q);
+	}
 
 	return ret;
 }