block, blk-mq: draining can't be skipped even if bypass_depth was non-zero

Currently, both blk_queue_bypass_start() and blk_mq_freeze_queue()
skip queue draining if bypass_depth was already above zero.  The
assumption is that the one which bumped the bypass_depth should have
performed draining already; however, there's nothing which prevents a
new instance of bypassing/freezing from starting before the previous
one finishes draining.  The current code may allow the later
bypassing/freezing instances to complete while there still are
in-flight requests which haven't finished draining.

Fix it by draining regardless of bypass_depth.  We still skip draining
from blk_queue_bypass_start() while the queue is initializing to avoid
introducing excessive delays during boot.  INIT_DONE setting is moved
above the initial blk_queue_bypass_end() so that bypassing attempts
can't slip inbetween.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9541f51..f4bdddd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -131,15 +131,12 @@ void blk_mq_drain_queue(struct request_queue *q)
  */
 static void blk_mq_freeze_queue(struct request_queue *q)
 {
-	bool drain;
-
 	spin_lock_irq(q->queue_lock);
-	drain = !q->bypass_depth++;
+	q->bypass_depth++;
 	queue_flag_set(QUEUE_FLAG_BYPASS, q);
 	spin_unlock_irq(q->queue_lock);
 
-	if (drain)
-		blk_mq_drain_queue(q);
+	blk_mq_drain_queue(q);
 }
 
 static void blk_mq_unfreeze_queue(struct request_queue *q)