Re: [PATCH V3 17/20] block: move debugfs/sysfs register out of freezing queue

[Ming Lei <ming.lei@redhat.com>]

On Fri, Apr 25, 2025 at 08:38:01PM +0200, Christoph Hellwig wrote:
> On Thu, Apr 24, 2025 at 11:21:40PM +0800, 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.
> 
> Please explain the why it's not required.  And talking about lockdep
> dependencies is not very useful - it either is an actual lock ordering
> issue or a fale positive, but lockdep is just the messenger.

Both kobject delete and debugfs unregister drains in-progress .show/.store
and read, they do not need to freeze queue.

Thanks, 
Ming