On 4/10/25 7:00 PM, Ming Lei wrote:
> Move debugfs/sysfs register out of freezing queue in
> __blk_mq_update_nr_hw_queues(), so that the following lockdep dependency
> can be killed:
>
> #2 (&q->q_usage_counter(io)#16){++++}-{0:0}:
> #1 (fs_reclaim){+.+.}-{0:0}:
> #0 (&sb->s_type->i_mutex_key#3){+.+.}-{4:4}: //debugfs
>
> And registering/un-registering debugfs/sysfs does not require queue to be
> frozen.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 7219b01764da..0fb72a698d77 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -4947,15 +4947,15 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
> if (set->nr_maps == 1 && nr_hw_queues == set->nr_hw_queues)
> return;
>
> - memflags = memalloc_noio_save();
> - list_for_each_entry(q, &set->tag_list, tag_set_list)
> - blk_mq_freeze_queue_nomemsave(q);
> -
> list_for_each_entry(q, &set->tag_list, tag_set_list) {
> blk_mq_debugfs_unregister_hctxs(q);
> blk_mq_sysfs_unregister_hctxs(q);
> }
As we removed hctx sysfs protection while un-registering it, this might
cause crash or other side-effect if simultaneously these sysfs attributes
are accessed. The read access of these attributes are still protected
using ->elevator_lock.
Thanks,
--Nilay
