blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe

[deliverable/linux.git] / block / blk-mq.c

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c88e6089746d82267c61d572baa25fe855704f22..df8e1e09dd172d9ab67dbd0a91e519c5c01919ef 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -119,7 +119,16 @@ void blk_mq_freeze_queue(struct request_queue *q)
        spin_unlock_irq(q->queue_lock);
 
        if (freeze) {
-               percpu_ref_kill(&q->mq_usage_counter);
+               /*
+                * XXX: Temporary kludge to work around SCSI blk-mq stall.
+                * SCSI synchronously creates and destroys many queues
+                * back-to-back during probe leading to lengthy stalls.
+                * This will be fixed by keeping ->mq_usage_counter in
+                * atomic mode until genhd registration, but, for now,
+                * let's work around using expedited synchronization.
+                */
+               __percpu_ref_kill_expedited(&q->mq_usage_counter);
+
                blk_mq_run_queues(q, false);
        }
        wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));