[PATCH] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()

[PATCH] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()

[Yu Kuai]

Commit 7f2799c546db ("blk-mq: cleanup shared tags case in
blk_mq_update_nr_requests()") moves blk_mq_tag_update_sched_shared_tags()
before q->nr_requests is updated, however, it's still using the old
q->nr_requests to resize tag depth.

Fix this problem by passing in expected new tag depth.

Fixes: 7f2799c546db ("blk-mq: cleanup shared tags case in blk_mq_update_nr_requests()")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-mq-sched.c | 2 +-
 block/blk-mq-tag.c   | 5 +++--
 block/blk-mq.c       | 2 +-
 block/blk-mq.h       | 3 ++-
 4 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index d06bb137a743..e0bed16485c3 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -557,7 +557,7 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e,
 	if (blk_mq_is_shared_tags(flags)) {
 		/* Shared tags are stored at index 0 in @et->tags. */
 		q->sched_shared_tags = et->tags[0];
-		blk_mq_tag_update_sched_shared_tags(q);
+		blk_mq_tag_update_sched_shared_tags(q, et->nr_requests);
 	}
 
 	queue_for_each_hw_ctx(q, hctx, i) {
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index c7a4d4b9cc87..5b664dbdf655 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -622,10 +622,11 @@ void blk_mq_tag_resize_shared_tags(struct blk_mq_tag_set *set, unsigned int size
 	sbitmap_queue_resize(&tags->bitmap_tags, size - set->reserved_tags);
 }
 
-void blk_mq_tag_update_sched_shared_tags(struct request_queue *q)
+void blk_mq_tag_update_sched_shared_tags(struct request_queue *q,
+					 unsigned int nr)
 {
 	sbitmap_queue_resize(&q->sched_shared_tags->bitmap_tags,
-			     q->nr_requests - q->tag_set->reserved_tags);
+			     nr - q->tag_set->reserved_tags);
 }
 
 /**
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 09f579414161..d626d32f6e57 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4941,7 +4941,7 @@ struct elevator_tags *blk_mq_update_nr_requests(struct request_queue *q,
 		 * tags can't grow, see blk_mq_alloc_sched_tags().
 		 */
 		if (q->elevator)
-			blk_mq_tag_update_sched_shared_tags(q);
+			blk_mq_tag_update_sched_shared_tags(q, nr);
 		else
 			blk_mq_tag_resize_shared_tags(set, nr);
 	} else if (!q->elevator) {
diff --git a/block/blk-mq.h b/block/blk-mq.h
index af42dc018808..c4fccdeb5441 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -186,7 +186,8 @@ void blk_mq_put_tag(struct blk_mq_tags *tags, struct blk_mq_ctx *ctx,
 void blk_mq_put_tags(struct blk_mq_tags *tags, int *tag_array, int nr_tags);
 void blk_mq_tag_resize_shared_tags(struct blk_mq_tag_set *set,
 		unsigned int size);
-void blk_mq_tag_update_sched_shared_tags(struct request_queue *q);
+void blk_mq_tag_update_sched_shared_tags(struct request_queue *q,
+					 unsigned int nr);
 
 void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool);
 void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn,
-- 
2.39.2

Re: [PATCH] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()

[Nilay Shroff]

On 10/15/25 7:18 AM, Yu Kuai wrote:
> Commit 7f2799c546db ("blk-mq: cleanup shared tags case in
> blk_mq_update_nr_requests()") moves blk_mq_tag_update_sched_shared_tags()
> before q->nr_requests is updated, however, it's still using the old
> q->nr_requests to resize tag depth.
> 
> Fix this problem by passing in expected new tag depth.
> 
> Fixes: 7f2799c546db ("blk-mq: cleanup shared tags case in blk_mq_update_nr_requests()")
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Looks good to me:
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>

Re: [PATCH] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()

[Ming Lei]

On Wed, Oct 15, 2025 at 9:56 AM Yu Kuai <yukuai3@huawei.com> wrote:
>
> Commit 7f2799c546db ("blk-mq: cleanup shared tags case in
> blk_mq_update_nr_requests()") moves blk_mq_tag_update_sched_shared_tags()
> before q->nr_requests is updated, however, it's still using the old
> q->nr_requests to resize tag depth.
>
> Fix this problem by passing in expected new tag depth.
>
> Fixes: 7f2799c546db ("blk-mq: cleanup shared tags case in blk_mq_update_nr_requests()")
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Re: [PATCH] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()

[Jens Axboe]

On 10/14/25 7:48 PM, Yu Kuai wrote:
> Commit 7f2799c546db ("blk-mq: cleanup shared tags case in
> blk_mq_update_nr_requests()") moves blk_mq_tag_update_sched_shared_tags()
> before q->nr_requests is updated, however, it's still using the old
> q->nr_requests to resize tag depth.
> 
> Fix this problem by passing in expected new tag depth.

Fix looks fine, but you really should add a Link to the bug report, and
also a Reported-by tag. I'll add those.

-- 
Jens Axboe

Re: [PATCH] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()

[Yu Kuai]

Hi,

在 2025/10/15 21:48, Jens Axboe 写道:
> On 10/14/25 7:48 PM, Yu Kuai wrote:
>> Commit 7f2799c546db ("blk-mq: cleanup shared tags case in
>> blk_mq_update_nr_requests()") moves blk_mq_tag_update_sched_shared_tags()
>> before q->nr_requests is updated, however, it's still using the old
>> q->nr_requests to resize tag depth.
>>
>> Fix this problem by passing in expected new tag depth.
> Fix looks fine, but you really should add a Link to the bug report, and
> also a Reported-by tag. I'll add those.

Thanks! Sorry that I do forget about this.
Kuai

Re: [PATCH] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()

[Jens Axboe]

On Wed, 15 Oct 2025 09:48:27 +0800, Yu Kuai wrote:
> Commit 7f2799c546db ("blk-mq: cleanup shared tags case in
> blk_mq_update_nr_requests()") moves blk_mq_tag_update_sched_shared_tags()
> before q->nr_requests is updated, however, it's still using the old
> q->nr_requests to resize tag depth.
> 
> Fix this problem by passing in expected new tag depth.
> 
> [...]

Applied, thanks!

[1/1] blk-mq: fix stale tag depth for shared sched tags in blk_mq_update_nr_requests()
      commit: dc96cefef0d3032c69e46a21b345c60e56b18934

Best regards,
-- 
Jens Axboe