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block: define alloc_sched_data and free_sched_data methods for kyber 

Currently, the Kyber elevator allocates its private data dynamically in
->init_sched and frees it in ->exit_sched. However, since ->init_sched
is invoked during elevator switch after acquiring both ->freeze_lock and
->elevator_lock, it may trigger the lockdep splat [1] due to dependency
on pcpu_alloc_mutex.

To resolve this, move the elevator data allocation and deallocation
logic from ->init_sched and ->exit_sched into the newly introduced
->alloc_sched_data and ->free_sched_data methods. These callbacks are
invoked before acquiring ->freeze_lock and ->elevator_lock, ensuring
that memory allocation happens safely without introducing additional
locking dependencies.

This change breaks the dependency chain involving pcpu_alloc_mutex and
prevents the reported lockdep warning.

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

Reported-by: Changhui Zhong <czhong@redhat.com>
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/all/CAGVVp+VNW4M-5DZMNoADp6o2VKFhi7KxWpTDkcnVyjO0=-D5+A@mail.gmail.com/
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Yu Kuai <yukuai@fnnas.com>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Nilay Shroff 2025-11-13 14:28:22 +05:30 committed by Jens Axboe
parent 0315476e78
commit d4c3ef56a1
1 changed files with 22 additions and 8 deletions
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30
block/kyber-iosched.c
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@ -409,30 +409,42 @@ static void kyber_depth_updated(struct request_queue *q)
static int kyber_init_sched(struct request_queue *q, struct elevator_queue *eq)
{
struct kyber_queue_data *kqd;
kqd = kyber_queue_data_alloc(q);
if (IS_ERR(kqd))
return PTR_ERR(kqd);
blk_stat_enable_accounting(q);
blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
eq->elevator_data = kqd;
q->elevator = eq;
kyber_depth_updated(q);
return 0;
}
static void *kyber_alloc_sched_data(struct request_queue *q)
{
struct kyber_queue_data *kqd;
kqd = kyber_queue_data_alloc(q);
if (IS_ERR(kqd))
return NULL;
return kqd;
}
static void kyber_exit_sched(struct elevator_queue *e)
{
struct kyber_queue_data *kqd = e->elevator_data;
int i;
timer_shutdown_sync(&kqd->timer);
blk_stat_disable_accounting(kqd->q);
}
static void kyber_free_sched_data(void *elv_data)
{
struct kyber_queue_data *kqd = elv_data;
int i;
if (!kqd)
return;
for (i = 0; i < KYBER_NUM_DOMAINS; i++)
sbitmap_queue_free(&kqd->domain_tokens[i]);
@ -1004,6 +1016,8 @@ static struct elevator_type kyber_sched = {
.exit_sched = kyber_exit_sched,
.init_hctx = kyber_init_hctx,
.exit_hctx = kyber_exit_hctx,
.alloc_sched_data = kyber_alloc_sched_data,
.free_sched_data = kyber_free_sched_data,
.limit_depth = kyber_limit_depth,
.bio_merge = kyber_bio_merge,
.prepare_request = kyber_prepare_request,