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/20201209052951.16136-2-bvanassche@acm.org
Fixes: 986d413b7c15 ("blk-mq: Enable support for runtime power management")
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Stanley Chu <stanley.chu@mediatek.com>
Co-developed-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/block/blk-pm.c b/block/blk-pm.c
index b85234d..17bd020 100644 (file)
--- a/block/blk-pm.c
+++ b/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;
 }