[PATCH] block: fix elv_update_nr_hw_queues() to reattach elevator

[PATCH] block: fix elv_update_nr_hw_queues() to reattach elevator

[Nilay Shroff]

When nr_hw_queues is updated, the elevator needs to be switched to
ensure that we exit elevator and reattach it to ensure that hctx->
sched_tags is correctly allocated for the new hardware queues.
However, elv_update_nr_hw_queues() currently only switches the
elevator if the queue is not registered. This is incorrect, as it
prevents reattaching the elevator after updating nr_hw_queues, which
in turn inhibits allocation of sched_tags.

Fix this by allowing the elevator switch if the queue is registered,
ensuring proper reattachment and resource allocation.

Fixes: 596dce110b7d ("block: simplify elevator reattachment for updating nr_hw_queues")
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
 block/elevator.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/elevator.c b/block/elevator.c
index f8d72bd20610..ab22542e6cf0 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -697,7 +697,7 @@ void elv_update_nr_hw_queues(struct request_queue *q)
 	WARN_ON_ONCE(q->mq_freeze_depth == 0);
 
 	mutex_lock(&q->elevator_lock);
-	if (q->elevator && !blk_queue_dying(q) && !blk_queue_registered(q)) {
+	if (q->elevator && !blk_queue_dying(q) && blk_queue_registered(q)) {
 		ctx.name = q->elevator->type->elevator_name;
 
 		/* force to reattach elevator after nr_hw_queue is updated */
-- 
2.49.0

Re: [PATCH] block: fix elv_update_nr_hw_queues() to reattach elevator

[Jens Axboe]

On Thu, 15 May 2025 19:14:39 +0530, Nilay Shroff wrote:
> When nr_hw_queues is updated, the elevator needs to be switched to
> ensure that we exit elevator and reattach it to ensure that hctx->
> sched_tags is correctly allocated for the new hardware queues.
> However, elv_update_nr_hw_queues() currently only switches the
> elevator if the queue is not registered. This is incorrect, as it
> prevents reattaching the elevator after updating nr_hw_queues, which
> in turn inhibits allocation of sched_tags.
> 
> [...]

Applied, thanks!

[1/1] block: fix elv_update_nr_hw_queues() to reattach elevator
      commit: 532b9e11b8540eb543ebec9cba851c5691e10b5b

Best regards,
-- 
Jens Axboe

Re: [PATCH] block: fix elv_update_nr_hw_queues() to reattach elevator

[Ming Lei]

On Thu, May 15, 2025 at 9:45 PM Nilay Shroff <nilay@linux.ibm.com> wrote:
>
> When nr_hw_queues is updated, the elevator needs to be switched to
> ensure that we exit elevator and reattach it to ensure that hctx->
> sched_tags is correctly allocated for the new hardware queues.
> However, elv_update_nr_hw_queues() currently only switches the
> elevator if the queue is not registered. This is incorrect, as it
> prevents reattaching the elevator after updating nr_hw_queues, which
> in turn inhibits allocation of sched_tags.
>
> Fix this by allowing the elevator switch if the queue is registered,
> ensuring proper reattachment and resource allocation.
>
> Fixes: 596dce110b7d ("block: simplify elevator reattachment for updating nr_hw_queues")
> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>

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

Thanks,