On Tue 21-12-21 11:21:35, Yu Kuai wrote:
> 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.
>
> Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
I'm just wondering, how can it happen that !bfq_bfqq_busy() queue is in
pos_tree? Because bfq_remove_request() takes care to remove bfqq from the
pos_tree...
Honza
> ---
> block/bfq-cgroup.c | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index 8e8cf6b3d946..822dd28ecf53 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -677,7 +677,6 @@ 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(old_parent);
>
> if (entity->parent &&
> entity->parent->last_bfqq_created == bfqq)
> @@ -690,11 +689,16 @@ 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);
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
