From: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
To: linux-kernel@vger.kernel.org
Cc: linux-block@vger.kernel.org, axboe@kernel.dk,
paolo.valente@linaro.org, oleksandr@natalenko.name,
Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Subject: [PATCH] block: bfq fix blkio cgroup leakage v3
Date: Mon, 27 Jul 2020 08:01:07 +0000 [thread overview]
Message-ID: <20200727080107.6431-1-dmtrmonakhov@yandex-team.ru> (raw)
In-Reply-To: <6422992afade0015d817a65c124e0c75@natalenko.name>
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.
We should drop group reference once it finaly removed from service
inside __bfq_bfqd_reset_in_service, as we do with queue entities.
##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:
changes since v2:
- use safe iteration macro to prevent freed object dereference.
Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
---
block/bfq-wf2q.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index 8113138..13b417a 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -635,14 +635,10 @@ static void bfq_idle_insert(struct bfq_service_tree *st,
* @entity: the entity being removed.
* @is_in_service: true if entity is currently the in-service entity.
*
- * Forget everything about @entity. In addition, if entity represents
- * a queue, and the latter is not in service, then release the service
- * reference to the queue (the one taken through bfq_get_entity). In
- * fact, in this case, there is really no more service reference to
- * the queue, as the latter is also outside any service tree. If,
- * instead, the queue is in service, then __bfq_bfqd_reset_in_service
- * will take care of putting the reference when the queue finally
- * stops being served.
+ * Forget everything about @entity. If entity is not in service, then release
+ * the service reference to the entity (the one taken through bfq_get_entity).
+ * If the entity is in service, then __bfq_bfqd_reset_in_service will take care
+ * of putting the reference when the entity finally stops being served.
*/
static void bfq_forget_entity(struct bfq_service_tree *st,
struct bfq_entity *entity,
@@ -1615,6 +1611,7 @@ bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
struct bfq_queue *in_serv_bfqq = bfqd->in_service_queue;
struct bfq_entity *in_serv_entity = &in_serv_bfqq->entity;
struct bfq_entity *entity = in_serv_entity;
+ struct bfq_entity *parent = NULL;
bfq_clear_bfqq_wait_request(in_serv_bfqq);
hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
@@ -1626,9 +1623,16 @@ bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
* execute the final step: reset in_service_entity along the
* path from entity to the root.
*/
- for_each_entity(entity)
+ for_each_entity_safe(entity, parent) {
entity->sched_data->in_service_entity = NULL;
-
+ /*
+ * Release bfq_groups reference if it was not released in
+ * bfq_forget_entity, which was taken in bfq_get_entity.
+ */
+ if (!bfq_entity_to_bfqq(entity) && !entity->on_st_or_in_serv)
+ bfqg_and_blkg_put(container_of(entity, struct bfq_group,
+ entity));
+ }
/*
* in_serv_entity is no longer in service, so, if it is in no
* service tree either, then release the service reference to
--
2.7.4
next prev parent reply other threads:[~2020-07-27 8:01 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-02 10:57 [PATCH] bfq: fix blkio cgroup leakage Dmitry Monakhov
2020-07-08 9:03 ` Dmitry Monakhov
2020-07-08 16:35 ` Paolo Valente
2020-07-08 17:48 ` Dmitry Monakhov
2020-07-09 7:19 ` Paolo Valente
2020-07-09 8:19 ` Dmitry Monakhov
2020-07-09 8:35 ` Paolo Valente
2020-07-20 12:19 ` Dmitry Monakhov
2020-07-20 16:34 ` Jens Axboe
2020-07-20 17:04 ` [PATCH] block: bfq fix blkio cgroup leakage v2 Dmitry Monakhov
2020-07-26 11:31 ` Oleksandr Natalenko
2020-07-27 8:01 ` Dmitry Monakhov [this message]
2020-07-27 9:17 ` [PATCH] block: bfq fix blkio cgroup leakage v3 Oleksandr Natalenko
2020-08-11 8:11 ` [PATCH] bfq: fix blkio cgroup leakage Dmitry Monakhov
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