linux-kernel - [PATCH v2] blk-mq: Fix blk_mq_tagset_busy

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Date:   Mon, 18 Oct 2021 17:41:23 +0800
From:   John Garry <john.garry@...wei.com>
To:     <axboe@...nel.dk>
CC:     <ming.lei@...hat.com>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <kashyap.desai@...adcom.com>,
        <hare@...e.de>, John Garry <john.garry@...wei.com>
Subject: [PATCH v2] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags

Since it is now possible for a tagset to share a single set of tags, the
iter function should not re-iter the tags for the count of #hw queues in
that case. Rather it should just iter once.

Fixes: e0fdf846c7bb ("blk-mq: Use shared tags for shared sbitmap support")
Reported-by: Kashyap Desai <kashyap.desai@...adcom.com>
Signed-off-by: John Garry <john.garry@...wei.com>
Reviewed-by: Ming Lei <ming.lei@...hat.com>
---
Diff to v1:
- Add Ming's RB tag

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 72a2724a4eee..c943b6529619 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -378,9 +378,12 @@ void blk_mq_all_tag_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 		busy_tag_iter_fn *fn, void *priv)
 {
-	int i;
+	unsigned int flags = tagset->flags;
+	int i, nr_tags;
+
+	nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues;
 
-	for (i = 0; i < tagset->nr_hw_queues; i++) {
+	for (i = 0; i < nr_tags; i++) {
 		if (tagset->tags && tagset->tags[i])
 			__blk_mq_all_tag_iter(tagset->tags[i], fn, priv,
 					      BT_TAG_ITER_STARTED);
-- 
2.26.2