From: Dmitry Monakhov dmtrmonakhov@yandex-team.ru
[ Upstream commit 2de791ab4918969d8108f15238a701968375f235 ]
Changes from v1: - update commit description with proper ref-accounting justification
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. In fact whole idea of original commit is wrong because bfq_group entity can not dissapear under us because it is referenced by child bfq_queue's entities from here: -> bfq_init_entity() ->bfqg_and_blkg_get(bfqg); ->entity->parent = bfqg->my_entity
-> bfq_put_queue(bfqq) FINAL_PUT ->bfqg_and_blkg_put(bfqq_group(bfqq)) ->kmem_cache_free(bfq_pool, bfqq);
So parent entity can not disappear while child entity is in tree, and child entities already has proper protection. This patch revert commit db37a34c563b ("block, bfq: get a ref to a group when adding it to a service tree")
bfq_group leak trace caused by bad commit: -> 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.
##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:
Fixes: db37a34c563b ("block, bfq: get a ref to a group when adding it to a service tree") Tested-by: Oleksandr Natalenko oleksandr@natalenko.name Signed-off-by: Dmitry Monakhov dmtrmonakhov@yandex-team.ru Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/bfq-cgroup.c | 2 +- block/bfq-iosched.h | 1 - block/bfq-wf2q.c | 12 ++---------- 3 files changed, 3 insertions(+), 12 deletions(-)
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c index 68882b9b8f11f..b791e2041e49b 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 cd224aaf9f52a..703895224562c 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 eb0e2a6daabe6..26776bdbdf360 100644 --- a/block/bfq-wf2q.c +++ b/block/bfq-wf2q.c @@ -533,9 +533,7 @@ static void bfq_get_entity(struct bfq_entity *entity) 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 +647,8 @@ 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)); }
/**