From: Yu Kuai <yukuai3@huawei.com>

This helper only support to iallocate the default number of requests,
add a new parameter to support specific number of requests.

Prepare to fix tags double free problem if nr_requests is grown by
queue sysfs attribute nr_requests.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-mq-sched.c | 11 +++++++----
 block/blk-mq-sched.h |  2 +-
 block/elevator.c     |  2 +-
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index e2ce4a28e6c9..9a8a0b5e04a9 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -454,7 +454,7 @@ void blk_mq_free_sched_tags_batch(struct xarray *et_table,
 }
 
 struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
-		unsigned int nr_hw_queues)
+		unsigned int nr_hw_queues, unsigned int nr_requests)
 {
 	unsigned int nr_tags;
 	int i;
@@ -475,8 +475,11 @@ struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
 	 * 128, since we don't split into sync/async like the old code
 	 * did. Additionally, this is a per-hw queue depth.
 	 */
-	et->nr_requests = 2 * min_t(unsigned int, set->queue_depth,
-			BLKDEV_DEFAULT_RQ);
+	if (nr_requests)
+		et->nr_requests = nr_requests;
+	else
+		et->nr_requests = 2 * min_t(unsigned int, set->queue_depth,
+				BLKDEV_DEFAULT_RQ);
 	et->nr_hw_queues = nr_hw_queues;
 
 	if (blk_mq_is_shared_tags(set->flags)) {
@@ -521,7 +524,7 @@ int blk_mq_alloc_sched_tags_batch(struct xarray *et_table,
 		 * concurrently.
 		 */
 		if (q->elevator) {
-			et = blk_mq_alloc_sched_tags(set, nr_hw_queues);
+			et = blk_mq_alloc_sched_tags(set, nr_hw_queues, 0);
 			if (!et)
 				goto out_unwind;
 			if (xa_insert(et_table, q->id, et, gfp))
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index b554e1d55950..0582d4bc3987 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -24,7 +24,7 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);
 void blk_mq_sched_free_rqs(struct request_queue *q);
 
 struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
-		unsigned int nr_hw_queues);
+		unsigned int nr_hw_queues, unsigned int nr_requests);
 int blk_mq_alloc_sched_tags_batch(struct xarray *et_table,
 		struct blk_mq_tag_set *set, unsigned int nr_hw_queues);
 void blk_mq_free_sched_tags(struct elevator_tags *et,
diff --git a/block/elevator.c b/block/elevator.c
index fe96c6f4753c..f8a04f32cbcf 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -669,7 +669,7 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 	lockdep_assert_held(&set->update_nr_hwq_lock);
 
 	if (strncmp(ctx->name, "none", 4)) {
-		ctx->et = blk_mq_alloc_sched_tags(set, set->nr_hw_queues);
+		ctx->et = blk_mq_alloc_sched_tags(set, set->nr_hw_queues, 0);
 		if (!ctx->et)
 			return -ENOMEM;
 	}
-- 
2.39.2

On Thu, Aug 14, 2025 at 11:35:07AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> This helper only support to iallocate the default number of requests,
> add a new parameter to support specific number of requests.
> 
> Prepare to fix tags double free problem if nr_requests is grown by
> queue sysfs attribute nr_requests.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  block/blk-mq-sched.c | 11 +++++++----
>  block/blk-mq-sched.h |  2 +-
>  block/elevator.c     |  2 +-
>  3 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index e2ce4a28e6c9..9a8a0b5e04a9 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -454,7 +454,7 @@ void blk_mq_free_sched_tags_batch(struct xarray *et_table,
>  }
>  
>  struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
> -		unsigned int nr_hw_queues)
> +		unsigned int nr_hw_queues, unsigned int nr_requests)
>  {
>  	unsigned int nr_tags;
>  	int i;
> @@ -475,8 +475,11 @@ struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
>  	 * 128, since we don't split into sync/async like the old code
>  	 * did. Additionally, this is a per-hw queue depth.
>  	 */
> -	et->nr_requests = 2 * min_t(unsigned int, set->queue_depth,
> -			BLKDEV_DEFAULT_RQ);
> +	if (nr_requests)
> +		et->nr_requests = nr_requests;
> +	else
> +		et->nr_requests = 2 * min_t(unsigned int, set->queue_depth,
> +				BLKDEV_DEFAULT_RQ);

It looks more readable to add helper blk_mq_default_nr_requests(),
and pass it from call sites directly, then people won't be confused
with the passed zero `nr_requests`.


Thanks, 
Ming

Hi,

在 2025/08/14 16:16, Ming Lei 写道:
>>   struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
>> -		unsigned int nr_hw_queues)
>> +		unsigned int nr_hw_queues, unsigned int nr_requests)
>>   {
>>   	unsigned int nr_tags;
>>   	int i;
>> @@ -475,8 +475,11 @@ struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
>>   	 * 128, since we don't split into sync/async like the old code
>>   	 * did. Additionally, this is a per-hw queue depth.
>>   	 */
>> -	et->nr_requests = 2 * min_t(unsigned int, set->queue_depth,
>> -			BLKDEV_DEFAULT_RQ);
>> +	if (nr_requests)
>> +		et->nr_requests = nr_requests;
>> +	else
>> +		et->nr_requests = 2 * min_t(unsigned int, set->queue_depth,
>> +				BLKDEV_DEFAULT_RQ);
> It looks more readable to add helper blk_mq_default_nr_requests(),
> and pass it from call sites directly, then people won't be confused
> with the passed zero `nr_requests`.

Yes, this sounds good.

Thanks for the review,
Kuai