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Subject[PATCH BUGFIX 3/4] block, bfq: make reparent_leaf_entity actually work only on leaf entities
Date
bfq_reparent_leaf_entity() reparents the input leaf entity (a leaf
entity represents just a bfq_queue in an entity tree). Yet, the input
entity is guaranteed to always be a leaf entity only in two-level
entity trees. In this respect, because of the error fixed by
commit 14afc5936197 ("block, bfq: fix overwrite of bfq_group pointer
in bfq_find_set_group()"), all (wrongly collapsed) entity trees happened
to actually have only two levels. After the latter commit, this does not
hold any longer.

This commit fixes this problem by modifying
bfq_reparent_leaf_entity(), so that it searches an active leaf entity
down the path that stems from the input entity. Such a leaf entity is
guaranteed to exist when bfq_reparent_leaf_entity() is invoked.

Tested-by: cki-project@redhat.com
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
block/bfq-cgroup.c | 48 ++++++++++++++++++++++++++++++----------------
1 file changed, 31 insertions(+), 17 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 72c6151ace96..efb89db7ba24 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -815,39 +815,53 @@ static void bfq_flush_idle_tree(struct bfq_service_tree *st)
/**
* bfq_reparent_leaf_entity - move leaf entity to the root_group.
* @bfqd: the device data structure with the root group.
- * @entity: the entity to move.
+ * @entity: the entity to move, if entity is a leaf; or the parent entity
+ * of an active leaf entity to move, if entity is not a leaf.
*/
static void bfq_reparent_leaf_entity(struct bfq_data *bfqd,
- struct bfq_entity *entity)
+ struct bfq_entity *entity,
+ int ioprio_class)
{
- struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
+ struct bfq_queue *bfqq;
+ struct bfq_entity *child_entity = entity;
+
+ while (child_entity->my_sched_data) { /* leaf not reached yet */
+ struct bfq_sched_data *child_sd = child_entity->my_sched_data;
+ struct bfq_service_tree *child_st = child_sd->service_tree +
+ ioprio_class;
+ struct rb_root *child_active = &child_st->active;

+ child_entity = bfq_entity_of(rb_first(child_active));
+
+ if (!child_entity)
+ child_entity = child_sd->in_service_entity;
+ }
+
+ bfqq = bfq_entity_to_bfqq(child_entity);
bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
}

/**
- * bfq_reparent_active_entities - move to the root group all active
- * entities.
+ * bfq_reparent_active_queues - move to the root group all active queues.
* @bfqd: the device data structure with the root group.
* @bfqg: the group to move from.
- * @st: the service tree with the entities.
+ * @st: the service tree to start the search from.
*/
-static void bfq_reparent_active_entities(struct bfq_data *bfqd,
- struct bfq_group *bfqg,
- struct bfq_service_tree *st)
+static void bfq_reparent_active_queues(struct bfq_data *bfqd,
+ struct bfq_group *bfqg,
+ struct bfq_service_tree *st,
+ int ioprio_class)
{
struct rb_root *active = &st->active;
- struct bfq_entity *entity = NULL;
-
- if (!RB_EMPTY_ROOT(&st->active))
- entity = bfq_entity_of(rb_first(active));
+ struct bfq_entity *entity;

- for (; entity ; entity = bfq_entity_of(rb_first(active)))
- bfq_reparent_leaf_entity(bfqd, entity);
+ while ((entity = bfq_entity_of(rb_first(active))))
+ bfq_reparent_leaf_entity(bfqd, entity, ioprio_class);

if (bfqg->sched_data.in_service_entity)
bfq_reparent_leaf_entity(bfqd,
- bfqg->sched_data.in_service_entity);
+ bfqg->sched_data.in_service_entity,
+ ioprio_class);
}

/**
@@ -898,7 +912,7 @@ static void bfq_pd_offline(struct blkg_policy_data *pd)
* There is no need to put the sync queues, as the
* scheduler has taken no reference.
*/
- bfq_reparent_active_entities(bfqd, bfqg, st);
+ bfq_reparent_active_queues(bfqd, bfqg, st, i);
}

__bfq_deactivate_entity(entity, false);
--
2.20.1
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