linux-kernel - [PATCH 04/13] blk-mq: Fix potential io hung for shared sbitmap per tagset

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Date:   Fri, 23 Dec 2022 20:52:14 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     axboe@...nel.dk, dwagner@...e.de, hare@...e.de,
        ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     hch@....de, john.garry@...wei.com, shikemeng@...weicloud.com
Subject: [PATCH 04/13] blk-mq: Fix potential io hung for shared sbitmap per tagset

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@...weicloud.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 202975f4d357..bfba0e151733 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1824,7 +1824,8 @@ 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);
 
 		/*
@@ -2094,7 +2095,8 @@ 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