Messages in this thread |  | | Date | Sun, 26 Jul 2020 13:31:37 +0200 | From | Oleksandr Natalenko <> | Subject | Re: [PATCH] block: bfq fix blkio cgroup leakage v2 |
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Hello.
On 20.07.2020 19:04, Dmitry Monakhov wrote: > 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: > > Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru> > --- > block/bfq-wf2q.c | 23 +++++++++++++---------- > 1 file changed, 13 insertions(+), 10 deletions(-) > > diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c > index 8113138..93b236c 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, > @@ -1626,9 +1622,16 @@ 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(entity) { > 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
As reported by one of my customers, this patch causes the following crash: [1]
[1] http://pix.academ.info/images/img/2020/07/26/52d097c02b6061657443bba92de75e8a.jpg
-- Oleksandr Natalenko (post-factum)
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