On 3/5/21 7:14 AM, John Garry wrote:
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 7ff1b20d58e7..5950fee490e8 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -358,11 +358,16 @@ void blk_mq_tagset_busy_iter(struct blk_mq_tag_set
> *tagset,
> {
> int i;
>
> + if (!atomic_inc_not_zero(&tagset->iter_usage_counter))
> + return;
> +
> for (i = 0; i < tagset->nr_hw_queues; i++) {
> if (tagset->tags && tagset->tags[i])
> __blk_mq_all_tag_iter(tagset->tags[i], fn, priv,
> BT_TAG_ITER_STARTED);
> }
> +
> + atomic_dec(&tagset->iter_usage_counter);
> }
> EXPORT_SYMBOL(blk_mq_tagset_busy_iter);
This changes the behavior of blk_mq_tagset_busy_iter(). What will e.g.
happen if the mtip driver calls blk_mq_tagset_busy_iter(&dd->tags,
mtip_abort_cmd, dd) concurrently with another blk_mq_tagset_busy_iter()
call and if that causes all mtip_abort_cmd() calls to be skipped?
> + while (atomic_cmpxchg(&set->iter_usage_counter, 1, 0) != 1);
Isn't it recommended to call cpu_relax() inside busy-waiting loops?
> blk_mq_sched_free_requests(q);
> __elevator_exit(q, e);
>
> + atomic_set(&set->iter_usage_counter, 1);
Can it happen that the above atomic_set() call happens while a
blk_mq_tagset_busy_iter() call is in progress? Should that atomic_set()
call perhaps be changed into an atomic_inc() call?
Thanks,
Bart.
