[PATCH 2/2] blk-mq: start to freeze queue just after setting dying

From: Ming Lei
Date: Thu Mar 09 2017 - 08:12:10 EST

Before commit 780db2071a(blk-mq: decouble blk-mq freezing
from generic bypassing), the dying flag is checked before
entering queue, and Tejun converts the checking into .mq_freeze_depth,
and assumes the counter is increased just after dying flag
is set. Unfortunately we doesn't do that in blk_set_queue_dying().

This patch calls blk_mq_freeze_queue_start() for blk-mq in
blk_set_queue_dying(), so that we can block new I/O coming
once the queue is set as dying.

Given blk_set_queue_dying() is always called in remove path
of block device, and queue will be cleaned up later, we don't
need to worry about undo of the counter.

Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx>
block/blk-core.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 0eeb99ef654f..559487e58296 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -500,9 +500,12 @@ void blk_set_queue_dying(struct request_queue *q)
queue_flag_set(QUEUE_FLAG_DYING, q);

- if (q->mq_ops)
+ if (q->mq_ops) {
- else {
+ /* block new I/O coming */
+ blk_mq_freeze_queue_start(q);
+ } else {
struct request_list *rl;