linux-kernel - Re: [PATCH] blk-mq: Fix blk_mq_tagset_busy

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Message-ID: <YWalYoOZmpkmAZNK@T590>
Date:   Wed, 13 Oct 2021 17:22:42 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, kashyap.desai@...adcom.com,
        hare@...e.de
Subject: Re: [PATCH] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags

On Wed, Oct 13, 2021 at 04:40:59PM +0800, John Garry wrote:
> Since it is now possible for a tagset to share a single set of tags, the
> iter function should not re-iter the tags for the count of #hw queues in
> that case. Rather it should just iter once.
> 
> Fixes: e0fdf846c7bb ("blk-mq: Use shared tags for shared sbitmap support")
> Reported-by: Kashyap Desai <kashyap.desai@...adcom.com>
> Signed-off-by: John Garry <john.garry@...wei.com>
> 
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 72a2724a4eee..c943b6529619 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -378,9 +378,12 @@ void blk_mq_all_tag_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
>  void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
>  		busy_tag_iter_fn *fn, void *priv)
>  {
> -	int i;
> +	unsigned int flags = tagset->flags;
> +	int i, nr_tags;
> +
> +	nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues;
>  
> -	for (i = 0; i < tagset->nr_hw_queues; i++) {
> +	for (i = 0; i < nr_tags; i++) {
>  		if (tagset->tags && tagset->tags[i])
>  			__blk_mq_all_tag_iter(tagset->tags[i], fn, priv,
>  					      BT_TAG_ITER_STARTED);

blk_mq_queue_tag_busy_iter() needn't such change?


Thanks,
Ming