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Commit 9dee8b3b authored by Paolo Valente's avatar Paolo Valente Committed by Jens Axboe
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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
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: default avatarPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent d87447d8

block/bfq-iosched.c

+13 −4
Original line number Diff line number Diff line
@@ -754,6 +754,7 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq, 


inc_counter:

	bfqq->weight_counter->num_active++;

	bfqq->ref++;

}



/*
@@ -778,6 +779,7 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd, 


reset_entity_pointer:

	bfqq->weight_counter = NULL;

	bfq_put_queue(bfqq);

}



/*
@@ -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,

				  &bfqd->queue_weights_tree);



	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, 
			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);

}



/*
@@ -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) */

block/bfq-wf2q.c

+3 −3
Original line number Diff line number Diff line
@@ -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)

		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);

}



/*