Messages in this thread | | | Subject | Re: [PATCH RFC] block, bfq: update pos_root for idle bfq_queue in bfq_bfqq_move() | From | "yukuai (C)" <> | Date | Sat, 18 Dec 2021 17:09:22 +0800 |
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在 2021/12/10 16:16, Yu Kuai 写道: > During code review, we found that if bfqq is not busy in > bfq_bfqq_move(), bfq_pos_tree_add_move() won't be called for the bfqq, > thus bfqq->pos_root still points to the old bfqg. However, the ref > that bfqq hold for the old bfqg will be released, so it's possible > that the old bfqg can be freed. This is problematic because the freed > bfqg can still be accessed by bfqq->pos_root. > > Fix the problem by calling bfq_pos_tree_add_move() for idle bfqq > as well. > Friendly ping ... > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > --- > block/bfq-cgroup.c | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) > > diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c > index 24a5c5329bcd..85f34c29b909 100644 > --- a/block/bfq-cgroup.c > +++ b/block/bfq-cgroup.c > @@ -645,6 +645,7 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, > struct bfq_group *bfqg) > { > struct bfq_entity *entity = &bfqq->entity; > + struct bfq_group *old_parent = bfqq_group(bfqq); > > /* > * Get extra reference to prevent bfqq from being freed in > @@ -666,7 +667,6 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, > bfq_deactivate_bfqq(bfqd, bfqq, false, false); > else if (entity->on_st_or_in_serv) > bfq_put_idle_entity(bfq_entity_service_tree(entity), entity); > - bfqg_and_blkg_put(bfqq_group(bfqq)); > > if (entity->parent && > entity->parent->last_bfqq_created == bfqq) > @@ -679,11 +679,16 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, > /* pin down bfqg and its associated blkg */ > bfqg_and_blkg_get(bfqg); > > - if (bfq_bfqq_busy(bfqq)) { > - if (unlikely(!bfqd->nonrot_with_queueing)) > - bfq_pos_tree_add_move(bfqd, bfqq); > + /* > + * Don't leave the pos_root to old bfqg, since the ref to old bfqg will > + * be released and the bfqg might be freed. > + */ > + if (unlikely(!bfqd->nonrot_with_queueing)) > + bfq_pos_tree_add_move(bfqd, bfqq); > + bfqg_and_blkg_put(old_parent); > + > + if (bfq_bfqq_busy(bfqq)) > bfq_activate_bfqq(bfqd, bfqq); > - } > > if (!bfqd->in_service_queue && !bfqd->rq_in_driver) > bfq_schedule_dispatch(bfqd); >
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