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.