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>

3 files changed, 10 insertions, 10 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 6f8dba161bfe..0d0bdd65b2d7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -438,14 +438,17 @@ static void __blk_drain_queue(struct request_queue *q, bool drain_all)
  */
 void blk_queue_bypass_start(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) {
+        /*
+         * Queues start drained.  Skip actual draining till init is
+         * complete.  This avoids lenghty delays during queue init which
+         * can happen many times during boot.
+         */
+        if (blk_queue_init_done(q)) {
                 spin_lock_irq(q->queue_lock);
                 __blk_drain_queue(q, false);
                 spin_unlock_irq(q->queue_lock);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9541f5111ba6..f4bdddd7ed99 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)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 23321fbab293..4db5abf96b9e 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -554,8 +554,8 @@ int blk_register_queue(struct gendisk *disk)
          * Initialization must be complete by now.  Finish the initial
          * bypass from queue allocation.
          */
-        blk_queue_bypass_end(q);
         queue_flag_set_unlocked(QUEUE_FLAG_INIT_DONE, q);
+        blk_queue_bypass_end(q);
 
         ret = blk_trace_init_sysfs(dev);
         if (ret)