[PATCH v4 04/14] blk-mq: Fix potential io hung for shared sbitmap per tagset

Kemeng Shi
2023-01-18T01:39:34Z

Commit f906a6a0f4268 ("blk-mq: improve tag waiting setup for non-shared
tags") mark restart for unshared tags for improvement. At that time,
tags is only shared betweens queues and we can check if tags is shared
by test BLK_MQ_F_TAG_SHARED.
Afterwards, commit 32bc15afed04b ("blk-mq: Facilitate a shared sbitmap per
tagset") enabled tags share betweens hctxs inside a queue. We only
mark restart for shared hctxs inside a queue and may cause io hung if
there is no tag currently allocated by hctxs going to be marked restart.
Wait on sbitmap_queue instead of mark restart for shared hctxs case to
fix this.

Fixes: 32bc15afed04 ("blk-mq: Facilitate a shared sbitmap per tagset")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
block/blk-mq.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 943f2ce1e674..6eb23bbe1787 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1831,7 +1831,8 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
wait_queue_entry_t *wait;
bool ret;

- if (!(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) {
+ if (!(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) &&
+ !(blk_mq_is_shared_tags(hctx->flags))) {
blk_mq_sched_mark_restart_hctx(hctx);

/*
@@ -2101,7 +2102,8 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
bool needs_restart;
/* For non-shared tags, the RESTART check will suffice */
bool no_tag = prep == PREP_DISPATCH_NO_TAG &&
- (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED);
+ ((hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) ||
+ blk_mq_is_shared_tags(hctx->flags));

if (nr_budgets)
blk_mq_release_budgets(q, list);
--
2.30.0