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block: Remove elevator_lock usage from blkg_conf frozen operations 

Remove the acquisition and release of q->elevator_lock in the
blkg_conf_open_bdev_frozen() and blkg_conf_exit_frozen() functions. The
elevator lock is no longer needed in these code paths since commit
78c271344b ("block: move wbt_enable_default() out of queue freezing
from sched ->exit()") which introduces `disk->rqos_state_mutex` for
protecting wbt state change, and not necessary to abuse elevator_lock
for this purpose.

This change helps to solve the lockdep warning reported from Yu Kuai[1].

Pass blktests/throtl with lockdep enabled.

Links: https://lore.kernel.org/linux-block/e5e7ac3f-2063-473a-aafb-4d8d43e5576e@yukuai.org.cn/ [1]
Fixes: commit 78c271344b ("block: move wbt_enable_default() out of queue freezing from sched ->exit()")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2025-10-15 18:30:39 +08:00 committed by Jens Axboe
parent dc96cefef0
commit 08823e89e3
1 changed files with 4 additions and 9 deletions
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13
block/blk-cgroup.c
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@ -812,8 +812,7 @@ int blkg_conf_open_bdev(struct blkg_conf_ctx *ctx)
} }
/* /*
* Similar to blkg_conf_open_bdev, but additionally freezes the queue, * Similar to blkg_conf_open_bdev, but additionally freezes the queue,
* acquires q->elevator_lock, and ensures the correct locking order * ensures the correct locking order between freeze queue and q->rq_qos_mutex.
* between q->elevator_lock and q->rq_qos_mutex.
* *
* This function returns negative error on failure. On success it returns * This function returns negative error on failure. On success it returns
* memflags which must be saved and later passed to blkg_conf_exit_frozen * memflags which must be saved and later passed to blkg_conf_exit_frozen
@ -834,13 +833,11 @@ unsigned long __must_check blkg_conf_open_bdev_frozen(struct blkg_conf_ctx *ctx)
* At this point, we haven’t started protecting anything related to QoS, * At this point, we haven’t started protecting anything related to QoS,
* so we release q->rq_qos_mutex here, which was first acquired in blkg_ * so we release q->rq_qos_mutex here, which was first acquired in blkg_
* conf_open_bdev. Later, we re-acquire q->rq_qos_mutex after freezing * conf_open_bdev. Later, we re-acquire q->rq_qos_mutex after freezing
* the queue and acquiring q->elevator_lock to maintain the correct * the queue to maintain the correct locking order.
* locking order.
*/ */
mutex_unlock(&ctx->bdev->bd_queue->rq_qos_mutex); mutex_unlock(&ctx->bdev->bd_queue->rq_qos_mutex);
memflags = blk_mq_freeze_queue(ctx->bdev->bd_queue); memflags = blk_mq_freeze_queue(ctx->bdev->bd_queue);
mutex_lock(&ctx->bdev->bd_queue->elevator_lock);
mutex_lock(&ctx->bdev->bd_queue->rq_qos_mutex); mutex_lock(&ctx->bdev->bd_queue->rq_qos_mutex);
return memflags; return memflags;
@ -995,9 +992,8 @@ void blkg_conf_exit(struct blkg_conf_ctx *ctx)
EXPORT_SYMBOL_GPL(blkg_conf_exit); EXPORT_SYMBOL_GPL(blkg_conf_exit);
/* /*
* Similar to blkg_conf_exit, but also unfreezes the queue and releases * Similar to blkg_conf_exit, but also unfreezes the queue. Should be used
* q->elevator_lock. Should be used when blkg_conf_open_bdev_frozen * when blkg_conf_open_bdev_frozen is used to open the bdev.
* is used to open the bdev.
*/ */
void blkg_conf_exit_frozen(struct blkg_conf_ctx *ctx, unsigned long memflags) void blkg_conf_exit_frozen(struct blkg_conf_ctx *ctx, unsigned long memflags)
{ {
@ -1005,7 +1001,6 @@ void blkg_conf_exit_frozen(struct blkg_conf_ctx *ctx, unsigned long memflags)
struct request_queue *q = ctx->bdev->bd_queue; struct request_queue *q = ctx->bdev->bd_queue;
blkg_conf_exit(ctx); blkg_conf_exit(ctx);
mutex_unlock(&q->elevator_lock);
blk_mq_unfreeze_queue(q, memflags); blk_mq_unfreeze_queue(q, memflags);
} }
} }