bt_wait_ptr() will increase 'wait_index', however, if blk_mq_get_tag()
get a tag successfully after bt_wait_ptr() is called and before
sbitmap_prepare_to_wait() is called, then the 'ws' is skipped. This
behavior might cause 8 waitqueues to be unbalanced.
Move bt_wait_ptr() later should reduce the problem when the disk is
under high io preesure.
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
block/blk-mq-tag.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 68ac23d0b640..a531351ab190 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -131,7 +131,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
{
struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
struct sbitmap_queue *bt;
- struct sbq_wait_state *ws;
+ struct sbq_wait_state *ws = NULL;
DEFINE_SBQ_WAIT(wait);
unsigned int tag_offset;
int tag;
@@ -155,7 +155,6 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
if (data->flags & BLK_MQ_REQ_NOWAIT)
return BLK_MQ_NO_TAG;
- ws = bt_wait_ptr(bt, data->hctx);
do {
struct sbitmap_queue *bt_prev;
@@ -173,7 +172,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
tag = __blk_mq_get_tag(data, bt);
if (tag != BLK_MQ_NO_TAG)
break;
-
+ if (!ws)
+ ws = bt_wait_ptr(bt, data->hctx);
sbitmap_prepare_to_wait(bt, ws, &wait, TASK_UNINTERRUPTIBLE);
tag = __blk_mq_get_tag(data, bt);
--
2.31.1
