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block: move elv_register[unregister]_queue out of elevator_lock

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Move elv_register[unregister]_queue out of ->elevator_lock & queue freezing,
so we can kill many lockdep warnings.

elv_register[unregister]_queue() is serialized, and just dealing with sysfs/
debugfs things, no need to be done with queue frozen:

- when it is called from adding disk, elevator switch isn't possible
  because ->queue_kobj isn't added yet

- when it is called from deleting disk, disable_elv_switch() is
  responsible for preventing new elevator switch and draining old
  elevator switch.

- when it is called from blk_mq_update_nr_hw_queues(), adding/removing
  disk and elevator switch can't be allowed or in-progress

With this change, elevator's ->exit() is called before calling
elv_unregister_queue, then user may call into ->show()/store() of elevator's
sysfs attributes, and we have covered this issue by adding `ELEVATOR_FLAG_DYNG`.

For blk-mq debugfs, hctx->sched_tags is always checked with ->elevator_lock by
debugfs code, meantime hctx->sched_tags is updated with ->elevator_lock, so
there isn't such issue.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250505141805.2751237-22-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2025-05-05 22:17:59 +08:00 committed by Jens Axboe
parent 21eed794ab
commit 559dc11143
2 changed files with 53 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
block/blk-mq.c
View File

@ -5041,11 +5041,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
blk_mq_debugfs_register_hctxs(q);
}
/* elv_update_nr_hw_queues() unfreeze queue for us */
list_for_each_entry(q, &set->tag_list, tag_set_list)
elv_update_nr_hw_queues(q);
list_for_each_entry(q, &set->tag_list, tag_set_list)
blk_mq_unfreeze_queue_nomemrestore(q);
memalloc_noio_restore(memflags);
/* Free the excess tags when nr_hw_queues shrink. */

68
block/elevator.c
View File

@ -49,6 +49,11 @@
struct elv_change_ctx {
const char *name;
bool no_uevent;
/* for unregistering old elevator */
struct elevator_queue *old;
/* for registering new elevator */
struct elevator_queue *new;
};
static DEFINE_SPINLOCK(elv_list_lock);
@ -158,14 +163,14 @@ static void elevator_exit(struct request_queue *q)
{
struct elevator_queue *e = q->elevator;
lockdep_assert_held(&q->elevator_lock);
ioc_clear_queue(q);
blk_mq_sched_free_rqs(q);
mutex_lock(&e->sysfs_lock);
blk_mq_exit_sched(q, e);
mutex_unlock(&e->sysfs_lock);
kobject_put(&e->kobj);
}
static inline void __elv_rqhash_del(struct request *rq)
@ -466,8 +471,6 @@ static int elv_register_queue(struct request_queue *q,
{
int error;
lockdep_assert_held(&q->elevator_lock);
error = kobject_add(&e->kobj, &q->disk->queue_kobj, "iosched");
if (!error) {
const struct elv_fs_entry *attr = e->type->elevator_attrs;
@ -494,8 +497,6 @@ static int elv_register_queue(struct request_queue *q,
static void elv_unregister_queue(struct request_queue *q,
struct elevator_queue *e)
{
lockdep_assert_held(&q->elevator_lock);
if (e && test_and_clear_bit(ELEVATOR_FLAG_REGISTERED, &e->flags)) {
kobject_uevent(&e->kobj, KOBJ_REMOVE);
kobject_del(&e->kobj);
@ -586,7 +587,7 @@ static int elevator_switch(struct request_queue *q, struct elv_change_ctx *ctx)
blk_mq_quiesce_queue(q);
if (q->elevator) {
elv_unregister_queue(q, q->elevator);
ctx->old = q->elevator;
elevator_exit(q);
}
@ -594,11 +595,7 @@ static int elevator_switch(struct request_queue *q, struct elv_change_ctx *ctx)
ret = blk_mq_init_sched(q, new_e);
if (ret)
goto out_unfreeze;
ret = elv_register_queue(q, q->elevator, !ctx->no_uevent);
if (ret) {
elevator_exit(q);
goto out_unfreeze;
}
ctx->new = q->elevator;
} else {
blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
q->elevator = NULL;
@ -619,6 +616,38 @@ static int elevator_switch(struct request_queue *q, struct elv_change_ctx *ctx)
return ret;
}
static void elv_exit_and_release(struct request_queue *q)
{
struct elevator_queue *e;
unsigned memflags;
memflags = blk_mq_freeze_queue(q);
mutex_lock(&q->elevator_lock);
e = q->elevator;
elevator_exit(q);
mutex_unlock(&q->elevator_lock);
blk_mq_unfreeze_queue(q, memflags);
if (e)
kobject_put(&e->kobj);
}
static int elevator_change_done(struct request_queue *q,
struct elv_change_ctx *ctx)
{
int ret = 0;
if (ctx->old) {
elv_unregister_queue(q, ctx->old);
kobject_put(&ctx->old->kobj);
}
if (ctx->new) {
ret = elv_register_queue(q, ctx->new, !ctx->no_uevent);
if (ret)
elv_exit_and_release(q);
}
return ret;
}
/*
* Switch this queue to the given IO scheduler.
*/
@ -645,6 +674,9 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
ret = elevator_switch(q, ctx);
mutex_unlock(&q->elevator_lock);
blk_mq_unfreeze_queue(q, memflags);
if (!ret)
ret = elevator_change_done(q, ctx);
return ret;
}
@ -654,18 +686,22 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
*/
void elv_update_nr_hw_queues(struct request_queue *q)
{
struct elv_change_ctx ctx = {};
int ret = -ENODEV;
WARN_ON_ONCE(q->mq_freeze_depth == 0);
mutex_lock(&q->elevator_lock);
if (q->elevator && !blk_queue_dying(q) && !blk_queue_registered(q)) {
struct elv_change_ctx ctx = {
.name = q->elevator->type->elevator_name,
};
ctx.name = q->elevator->type->elevator_name;
/* force to reattach elevator after nr_hw_queue is updated */
elevator_switch(q, &ctx);
ret = elevator_switch(q, &ctx);
}
mutex_unlock(&q->elevator_lock);
blk_mq_unfreeze_queue_nomemrestore(q);
if (!ret)
WARN_ON_ONCE(elevator_change_done(q, &ctx));
}
/*