commit db37a34c563b ("block, bfq: get a ref to a group when adding it to a service tree")
introduce leak forbfq_group and blkcg_gq objects because of get/put
imbalance. See trace balow:
-> blkg_alloc
-> bfq_pq_alloc
-> bfqg_get (+1)
->bfq_activate_bfqq
->bfq_activate_requeue_entity
-> __bfq_activate_entity
->bfq_get_entity
->bfqg_and_blkg_get (+1) <==== : Note1
->bfq_del_bfqq_busy
->bfq_deactivate_entity+0x53/0xc0 [bfq]
->__bfq_deactivate_entity+0x1b8/0x210 [bfq]
-> bfq_forget_entity(is_in_service = true)
entity->on_st_or_in_serv = false <=== :Note2
if (is_in_service)
return; ==> do not touch reference
-> blkcg_css_offline
-> blkcg_destroy_blkgs
-> blkg_destroy
-> bfq_pd_offline
-> __bfq_deactivate_entity
if (!entity->on_st_or_in_serv) /* true, because (Note2)
return false;
-> bfq_pd_free
-> bfqg_put() (-1, byt bfqg->ref == 2) because of (Note2)
So bfq_group and blkcg_gq will leak forever, see test-case below.
If fact bfq_group objects reference counting are quite different
from bfq_queue. bfq_groups object are referenced by blkcg_gq via
blkg_policy_data pointer, so neither nor blkg_get() neither bfqg_get
required here.
This patch drop commit db37a34c563b ("block, bfq: get a ref to a group when adding it to a service tree")
and add corresponding comment.
##TESTCASE_BEGIN:
#!/bin/bash
max_iters=${1:-100}
#prep cgroup mounts
mount -t tmpfs cgroup_root /sys/fs/cgroup
mkdir /sys/fs/cgroup/blkio
mount -t cgroup -o blkio none /sys/fs/cgroup/blkio
# Prepare blkdev
grep blkio /proc/cgroups
truncate -s 1M img
losetup /dev/loop0 img
echo bfq > /sys/block/loop0/queue/scheduler
grep blkio /proc/cgroups
for ((i=0;i<max_iters;i++))
do
mkdir -p /sys/fs/cgroup/blkio/a
echo 0 > /sys/fs/cgroup/blkio/a/cgroup.procs
dd if=/dev/loop0 bs=4k count=1 of=/dev/null iflag=direct 2> /dev/null
echo 0 > /sys/fs/cgroup/blkio/cgroup.procs
rmdir /sys/fs/cgroup/blkio/a
grep blkio /proc/cgroups
done
##TESTCASE_END:
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxx>
---
block/bfq-cgroup.c | 2 +-
block/bfq-iosched.h | 1 -
block/bfq-wf2q.c | 15 +++++----------
3 files changed, 6 insertions(+), 12 deletions(-)
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 68882b9..b791e20 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);
}
-void bfqg_and_blkg_get(struct bfq_group *bfqg)
+static 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 cd224aa..7038952 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -986,7 +986,6 @@ 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 34ad095..6a363bb 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -529,13 +529,14 @@ static void bfq_get_entity(struct bfq_entity *entity)
{
struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
+ /* Grab reference only for bfq_queue's objects, bfq_group ones
+ * are owned by blkcg_gq
+ */
if (bfqq) {
bfqq->ref++;
bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
bfqq, bfqq->ref);
- } else
- bfqg_and_blkg_get(container_of(entity, struct bfq_group,
- entity));
+ }
}
/**
@@ -649,14 +650,8 @@ static void bfq_forget_entity(struct bfq_service_tree *st,
entity->on_st_or_in_serv = false;
st->wsum -= entity->weight;
- if (is_in_service)
- return;
-
- if (bfqq)
+ if (bfqq && !is_in_service)
bfq_put_queue(bfqq);
- else
- bfqg_and_blkg_put(container_of(entity, struct bfq_group,
- entity));
}
/**
--
2.7.4
