Re: [PATCH] block: remove per-disk debugfs files in blk_unregister_queue

Hannes Reinecke
2022-05-24T09:29:11Z

On 5/24/22 10:33, Christoph Hellwig wrote:
> The block debugfs files are created in blk_register_queue, which is
> called by add_disk and use a naming scheme based on the disk_name.
> After del_gendisk returns that name can be reused and thus we must not
> leave these debugfs files around, otherwise the kernel is unhappy
> and spews messages like:
>
> Directory XXXXX with parent 'block' already present!
>
> and the newly created devices will not have working debugfs files.
>
> Move the unregistration to blk_unregister_queue instead (which matches
> the sysfs unregistration) to make sure the debugfs life time rules match
> those of the disk name.
>
> As part of the move also make sure the whole debugfs unregistration is
> inside a single debugfs_mutex critical section.
>
> Note that this breaks blktests block/002, which checks that the debugfs
> directory has not been removed while blktests is running, but that
> particular check should simply be removed from the test case.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> block/blk-mq-debugfs.c | 8 ++------
> block/blk-mq-debugfs.h | 5 -----
> block/blk-rq-qos.c | 2 --
> block/blk-sysfs.c | 15 +++++++--------
> kernel/trace/blktrace.c | 3 ---
> 5 files changed, 9 insertions(+), 24 deletions(-)
>
> diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
> index 7e4136a60e1cc..f7eaa5405e4b5 100644
> --- a/block/blk-mq-debugfs.c
> +++ b/block/blk-mq-debugfs.c
> @@ -713,6 +713,8 @@ void blk_mq_debugfs_register(struct request_queue *q)
>
> void blk_mq_debugfs_unregister(struct request_queue *q)
> {
> + /* all entries were removed by the caller */
> + q->rqos_debugfs_dir = NULL;
> q->sched_debugfs_dir = NULL;
> }
>
> @@ -833,12 +835,6 @@ void blk_mq_debugfs_register_rqos(struct rq_qos *rqos)
> debugfs_create_files(rqos->debugfs_dir, rqos, rqos->ops->debugfs_attrs);
> }
>
> -void blk_mq_debugfs_unregister_queue_rqos(struct request_queue *q)
> -{
> - debugfs_remove_recursive(q->rqos_debugfs_dir);
> - q->rqos_debugfs_dir = NULL;
> -}
> -
> void blk_mq_debugfs_register_sched_hctx(struct request_queue *q,
> struct blk_mq_hw_ctx *hctx)
> {
> diff --git a/block/blk-mq-debugfs.h b/block/blk-mq-debugfs.h
> index 69918f4170d69..401e9e9da640b 100644
> --- a/block/blk-mq-debugfs.h
> +++ b/block/blk-mq-debugfs.h
> @@ -36,7 +36,6 @@ void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx);
>
> void blk_mq_debugfs_register_rqos(struct rq_qos *rqos);
> void blk_mq_debugfs_unregister_rqos(struct rq_qos *rqos);
> -void blk_mq_debugfs_unregister_queue_rqos(struct request_queue *q);
> #else
> static inline void blk_mq_debugfs_register(struct request_queue *q)
> {
> @@ -87,10 +86,6 @@ static inline void blk_mq_debugfs_register_rqos(struct rq_qos *rqos)
> static inline void blk_mq_debugfs_unregister_rqos(struct rq_qos *rqos)
> {
> }
> -
> -static inline void blk_mq_debugfs_unregister_queue_rqos(struct request_queue *q)
> -{
> -}
> #endif
>
> #ifdef CONFIG_BLK_DEBUG_FS_ZONED
> diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
> index e83af7bc75919..d3a75693adbf4 100644
> --- a/block/blk-rq-qos.c
> +++ b/block/blk-rq-qos.c
> @@ -294,8 +294,6 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data,
>
> void rq_qos_exit(struct request_queue *q)
> {
> - blk_mq_debugfs_unregister_queue_rqos(q);
> -
> while (q->rq_qos) {
> struct rq_qos *rqos = q->rq_qos;
> q->rq_qos = rqos->next;
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 88bd41d4cb593..c02fec8e9a3f6 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -779,14 +779,6 @@ static void blk_release_queue(struct kobject *kobj)
> if (queue_is_mq(q))
> blk_mq_release(q);
>
> - blk_trace_shutdown(q);
> - mutex_lock(&q->debugfs_mutex);
> - debugfs_remove_recursive(q->debugfs_dir);
> - mutex_unlock(&q->debugfs_mutex);
> -
> - if (queue_is_mq(q))
> - blk_mq_debugfs_unregister(q);
> -
> bioset_exit(&q->bio_split);
>
> if (blk_queue_has_srcu(q))
> @@ -951,5 +943,12 @@ void blk_unregister_queue(struct gendisk *disk)
>
> mutex_unlock(&q->sysfs_dir_lock);
>
> + mutex_lock(&q->debugfs_mutex);
> + blk_trace_shutdown(q);
> + debugfs_remove_recursive(q->debugfs_dir);
> + if (queue_is_mq(q))
> + blk_mq_debugfs_unregister(q);
> + mutex_unlock(&q->debugfs_mutex);
> +
Odd.
Calling debugfs_remove_recursive(q->debugfs_dir) for all queue types,
but setting q->debugfs_dir to NULL only for mq?
Care to explain?

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
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