Re: [PATCH 08/12] block: don't remove hctx debugfs dir from blk_mq_exit_queue

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

On Tue, Feb 22, 2022 at 08:06:31PM -0800, Bart Van Assche wrote:
> On 2/22/22 06:14, Christoph Hellwig wrote:
> > From: Ming Lei <ming.lei@redhat.com>
> > 
> > The queue's top debugfs dir is removed from blk_release_queue(), so all
> > hctx's debugfs dirs are removed from there. Given blk_mq_exit_queue()
> > is only called from blk_cleanup_queue(), it isn't necessary to remove
> > hctx debugfs from blk_mq_exit_queue().
> > 
> > So remove it from blk_mq_exit_queue().
> > 
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >   block/blk-mq.c | 1 -
> >   1 file changed, 1 deletion(-)
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 63e2d3fd60946..540c8da30da72 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -3425,7 +3425,6 @@ static void blk_mq_exit_hw_queues(struct request_queue *q,
> >   	queue_for_each_hw_ctx(q, hctx, i) {
> >   		if (i == nr_queue)
> >   			break;
> > -		blk_mq_debugfs_unregister_hctx(hctx);
> >   		blk_mq_exit_hctx(q, set, hctx, i);
> >   	}
> >   }
> 
> What will happen if a new queue with the same name as a removed queue is
> created before blk_release_queue() for the removed queue has finished? Will
> that cause registration of debugfs attributes for the newly created queue to
> fail?

That may happen, but not related with this patch, since this patch just
delays removing of hctx's debug entry. And q->debugfs_dir is removed
from blk_release_queue().

So far, request queue doesn't has name, and just uses the disk's name
for creating debugfs entry. The trouble should have been there for long
time.


Thanks,
Ming