linux-kernel - [PATCH BUGFIX 5/6] block, bfq: get a ref to a group when adding it to a service tree

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Date:   Fri, 31 Jan 2020 10:24:08 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        bfq-iosched@...glegroups.com, oleksandr@...alenko.name,
        patdung100@...il.com, cevich@...hat.com,
        Paolo Valente <paolo.valente@...aro.org>
Subject: [PATCH BUGFIX 5/6] block, bfq: get a ref to a group when adding it to a service tree

BFQ schedules generic entities, which may represent either bfq_queues
or groups of bfq_queues. When an entity is inserted into a service
tree, a reference must be taken, to make sure that the entity does not
disappear while still referred in the tree. Unfortunately, such a
reference is mistakenly taken only if the entity represents a
bfq_queue. This commit takes a reference also in case the entity
represents a group.

Tested-by: Chris Evich <cevich@...hat.com>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 block/bfq-cgroup.c  |  2 +-
 block/bfq-iosched.h |  1 +
 block/bfq-wf2q.c    | 16 +++++++++++++++-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index c818c64766e5..f85b25fd06f2 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -332,7 +332,7 @@ static void bfqg_put(struct bfq_group *bfqg)
 		kfree(bfqg);
 }
 
-static void bfqg_and_blkg_get(struct bfq_group *bfqg)
+void bfqg_and_blkg_get(struct bfq_group *bfqg)
 {
 	/* see comments in bfq_bic_update_cgroup for why refcounting bfqg */
 	bfqg_get(bfqg);
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index f1cb89def7f8..b9627ec7007b 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -984,6 +984,7 @@ struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd,
 struct blkcg_gq *bfqg_to_blkg(struct bfq_group *bfqg);
 struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
 struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd, int node);
+void bfqg_and_blkg_get(struct bfq_group *bfqg);
 void bfqg_and_blkg_put(struct bfq_group *bfqg);
 
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index 26776bdbdf36..ef06e0d34b5b 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -533,7 +533,13 @@ static void bfq_get_entity(struct bfq_entity *entity)
 		bfqq->ref++;
 		bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
 			     bfqq, bfqq->ref);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	} else
+		bfqg_and_blkg_get(container_of(entity, struct bfq_group,
+					       entity));
+#else
 	}
+#endif
 }
 
 /**
@@ -647,8 +653,16 @@ static void bfq_forget_entity(struct bfq_service_tree *st,
 
 	entity->on_st_or_in_serv = false;
 	st->wsum -= entity->weight;
-	if (bfqq && !is_in_service)
+	if (is_in_service)
+		return;
+
+	if (bfqq)
 		bfq_put_queue(bfqq);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	else
+		bfqg_and_blkg_put(container_of(entity, struct bfq_group,
+					       entity));
+#endif
 }
 
 /**
-- 
2.20.1