-bouncing mail. This one is for 4.14. Apologies. Giuliano. On Mon, 8 Jun 2020 at 10:39, Giuliano Procida <gprocida@xxxxxxxxxx> wrote: > > From: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx> > > commit f5bbbbe4d63577026f908a809f22f5fd5a90ea1f upstream. > > For blk-mq, part_in_flight/rw will invoke blk_mq_in_flight/rw to > account the inflight requests. It will access the queue_hw_ctx and > nr_hw_queues w/o any protection. When updating nr_hw_queues and > blk_mq_in_flight/rw occur concurrently, panic comes up. > > Before update nr_hw_queues, the q will be frozen. So we could use > q_usage_counter to avoid the race. percpu_ref_is_zero is used here > so that we will not miss any in-flight request. The access to > nr_hw_queues and queue_hw_ctx in blk_mq_queue_tag_busy_iter are > under rcu critical section, __blk_mq_update_nr_hw_queues could use > synchronize_rcu to ensure the zeroed q_usage_counter to be globally > visible. > > Backporting Notes > > This is a re-backport, landing synchronize_rcu in the right place. > > Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx> > Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> > Signed-off-by: Giuliano Procida <gprocida@xxxxxxxxxx> > --- > block/blk-mq.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 9d53f476c517..cf56bdad2e06 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2738,6 +2738,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, > > list_for_each_entry(q, &set->tag_list, tag_set_list) > blk_mq_freeze_queue(q); > + /* > + * Sync with blk_mq_queue_tag_busy_iter. > + */ > + synchronize_rcu(); > > set->nr_hw_queues = nr_hw_queues; > blk_mq_update_queue_map(set); > @@ -2748,10 +2752,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, > > list_for_each_entry(q, &set->tag_list, tag_set_list) > blk_mq_unfreeze_queue(q); > - /* > - * Sync with blk_mq_queue_tag_busy_iter. > - */ > - synchronize_rcu(); > } > > void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues) > -- > 2.27.0.278.ge193c7cf3a9-goog >
