block: introduce alloc_sched_data and free_sched_data elevator methods

The recent lockdep splat [1] highlights a potential deadlock risk
involving ->elevator_lock and ->freeze_lock dependencies on -pcpu_alloc_
mutex. The trace shows that the issue occurs when the Kyber scheduler
allocates dynamic memory for its elevator data during initialization.

To address this, introduce two new elevator operation callbacks:
->alloc_sched_data and ->free_sched_data. The subsequent patch would
build upon these newly introduced methods to suppress lockdep splat[1].

[1] https://lore.kernel.org/all/CAGVVp+VNW4M-5DZMNoADp6o2VKFhi7KxWpTDkcnVyjO0=-D5+A@mail.gmail.com/

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Nilay Shroff
2025-11-13 14:28:20 +05:30
committed by Jens Axboe
parent 04728ce909
commit 61019afdf6
2 changed files with 26 additions and 0 deletions

View File

@@ -58,6 +58,8 @@ struct elevator_mq_ops {
int (*init_hctx)(struct blk_mq_hw_ctx *, unsigned int);
void (*exit_hctx)(struct blk_mq_hw_ctx *, unsigned int);
void (*depth_updated)(struct request_queue *);
void *(*alloc_sched_data)(struct request_queue *);
void (*free_sched_data)(void *);
bool (*allow_merge)(struct request_queue *, struct request *, struct bio *);
bool (*bio_merge)(struct request_queue *, struct bio *, unsigned int);