From: Paolo Valente paolo.valente@linaro.org
[ Upstream commit 9dee8b3b057e1da26f85f1842f2aaf3bb200fb94 ]
bfq maintains an ordered list, through a red-black tree, of unique weights of active bfq_queues. This list is used to detect whether there are active queues with differentiated weights. The weight of a queue is removed from the list when both the following two conditions become true:
(1) the bfq_queue is flagged as inactive (2) the has no in-flight request any longer;
Unfortunately, in the rare cases where condition (2) becomes true before condition (1), the removal fails, because the function to remove the weight of the queue (bfq_weights_tree_remove) is rightly invoked in the path that deactivates the bfq_queue, but mistakenly invoked *before* the function that actually performs the deactivation (bfq_deactivate_bfqq).
This commits moves the invocation of bfq_weights_tree_remove for condition (1) to after bfq_deactivate_bfqq. As a consequence of this move, it is necessary to add a further reference to the queue when the weight of a queue is added, because the queue might otherwise be freed before bfq_weights_tree_remove is invoked. This commit adds this reference and makes all related modifications.
Signed-off-by: Paolo Valente paolo.valente@linaro.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/bfq-iosched.c | 17 +++++++++++++---- block/bfq-wf2q.c | 6 +++--- 2 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index f010810c095f..e5ed28629271 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -747,6 +747,7 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
inc_counter: bfqq->weight_counter->num_active++; + bfqq->ref++; }
/* @@ -771,6 +772,7 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd,
reset_entity_pointer: bfqq->weight_counter = NULL; + bfq_put_queue(bfqq); }
/* @@ -782,9 +784,6 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd, { struct bfq_entity *entity = bfqq->entity.parent;
- __bfq_weights_tree_remove(bfqd, bfqq, - &bfqd->queue_weights_tree); - for_each_entity(entity) { struct bfq_sched_data *sd = entity->my_sched_data;
@@ -818,6 +817,15 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd, bfqd->num_groups_with_pending_reqs--; } } + + /* + * Next function is invoked last, because it causes bfqq to be + * freed if the following holds: bfqq is not in service and + * has no dispatched request. DO NOT use bfqq after the next + * function invocation. + */ + __bfq_weights_tree_remove(bfqd, bfqq, + &bfqd->queue_weights_tree); }
/* @@ -1011,7 +1019,8 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
static int bfqq_process_refs(struct bfq_queue *bfqq) { - return bfqq->ref - bfqq->allocated - bfqq->entity.on_st; + return bfqq->ref - bfqq->allocated - bfqq->entity.on_st - + (bfqq->weight_counter != NULL); }
/* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */ diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c index 72adbbe975d5..4aab1a8191f0 100644 --- a/block/bfq-wf2q.c +++ b/block/bfq-wf2q.c @@ -1667,15 +1667,15 @@ void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfqd->busy_queues--;
- if (!bfqq->dispatched) - bfq_weights_tree_remove(bfqd, bfqq); - if (bfqq->wr_coeff > 1) bfqd->wr_busy_queues--;
bfqg_stats_update_dequeue(bfqq_group(bfqq));
bfq_deactivate_bfqq(bfqd, bfqq, true, expiration); + + if (!bfqq->dispatched) + bfq_weights_tree_remove(bfqd, bfqq); }
/*