Commit 9dee8b3b authored by Paolo Valente's avatar Paolo Valente Committed by Jens Axboe

block, bfq: fix queue removal from weights tree

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

(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: 's avatarPaolo Valente <>
Signed-off-by: 's avatarJens Axboe <>
parent d87447d8
......@@ -754,6 +754,7 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
......@@ -778,6 +779,7 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd,
bfqq->weight_counter = NULL;
......@@ -789,9 +791,6 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
struct bfq_entity *entity = bfqq->entity.parent;
__bfq_weights_tree_remove(bfqd, bfqq,
for_each_entity(entity) {
struct bfq_sched_data *sd = entity->my_sched_data;
......@@ -825,6 +824,15 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
* 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,
......@@ -1020,7 +1028,8 @@ 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) */
......@@ -1673,15 +1673,15 @@ void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfqd->busy_queues[bfqq->ioprio_class - 1]--;
if (!bfqq->dispatched)
bfq_weights_tree_remove(bfqd, bfqq);
if (bfqq->wr_coeff > 1)
bfq_deactivate_bfqq(bfqd, bfqq, true, expiration);
if (!bfqq->dispatched)
bfq_weights_tree_remove(bfqd, bfqq);
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