[PATCH 4/4] blk-mq: use blk_queue_enter/exit to protect debugfs file creation

[Bart Van Assche]

On 2/9/26 12:29 AM, Yu Kuai wrote:
> diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
> index faeaa1fc86a7..03583d0d3972 100644
> --- a/block/blk-mq-debugfs.c
> +++ b/block/blk-mq-debugfs.c
> @@ -613,11 +613,6 @@ static void debugfs_create_files(struct request_queue *q, struct dentry *parent,
>   				 const struct blk_mq_debugfs_attr *attr)
>   {
>   	lockdep_assert_held(&q->debugfs_mutex);
> -	/*
> -	 * Creating new debugfs entries with queue freezed has the risk of
> -	 * deadlock.
> -	 */
> -	WARN_ON_ONCE(q->mq_freeze_depth != 0);
>   	/*
>   	 * debugfs_mutex should not be nested under other locks that can be
>   	 * grabbed while queue is frozen.

The above looks fine to me.

> @@ -628,9 +623,19 @@ static void debugfs_create_files(struct request_queue *q, struct dentry *parent,
>   	if (IS_ERR_OR_NULL(parent))
>   		return;
>   
> +	/*
> +	 * Avoid creating debugfs files while the queue is frozen, wait for
> +	 * the queue to be unfrozen and prevent new freeze while creating
> +	 * debugfs files.
> +	 */
> +	if (blk_queue_enter(q, 0))
> +		return;
> +
>   	for (; attr->name; attr++)
>   		debugfs_create_file_aux(attr->name, attr->mode, parent,
>   				    (void *)attr, data, &blk_mq_debugfs_fops);
> +
> +	blk_queue_exit(q);
>   }

This is not clear to me. Why are concurrent queue freezes not allowed
while debugfs attributes are created? I don't see any code in debugfs
that calls back into the block layer while creating debugfs attributes?
Did I perhaps overlook something?

Thanks,

Bart.