On Wed, Feb 05, 2025 at 08:14:47PM +0530, Nilay Shroff wrote:
>
> static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
> @@ -5006,8 +5008,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
> return;
>
> memflags = memalloc_noio_save();
> - list_for_each_entry(q, &set->tag_list, tag_set_list)
> + list_for_each_entry(q, &set->tag_list, tag_set_list) {
> + mutex_lock(&q->sysfs_lock);
This now means we hold up to number of request queues sysfs_lock
at the same time. I doubt lockdep will be happy about this.
Did you test this patch with a multi-namespace nvme device or
a multi-LU per host SCSI setup?
I suspect the answer here is to (ab)use the tag_list_lock for
scheduler updates - while the scope is too broad for just
changing it on a single queue it is a rate operation and it
solves the mess in __blk_mq_update_nr_hw_queues.
