From: Carlo Nonato carlo.nonato95@gmail.com
[ Upstream commit 14afc59361976c0ba39e3a9589c3eaa43ebc7e1d ]
The bfq_find_set_group() function takes as input a blkcg (which represents a cgroup) and retrieves the corresponding bfq_group, then it updates the bfq internal group hierarchy (see comments inside the function for why this is needed) and finally it returns the bfq_group. In the hierarchy update cycle, the pointer holding the correct bfq_group that has to be returned is mistakenly used to traverse the hierarchy bottom to top, meaning that in each iteration it gets overwritten with the parent of the current group. Since the update cycle stops at root's children (depth = 2), the overwrite becomes a problem only if the blkcg describes a cgroup at a hierarchy level deeper than that (depth > 2). In this case the root's child that happens to be also an ancestor of the correct bfq_group is returned. The main consequence is that processes contained in a cgroup at depth greater than 2 are wrongly placed in the group described above by BFQ.
This commits fixes this problem by using a different bfq_group pointer in the update cycle in order to avoid the overwrite of the variable holding the original group reference.
Reported-by: Kwon Je Oh kwonje.oh2@gmail.com Signed-off-by: Carlo Nonato carlo.nonato95@gmail.com Signed-off-by: Paolo Valente paolo.valente@linaro.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/bfq-cgroup.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c index d0e36d6522649..86cd718e0380b 100644 --- a/block/bfq-cgroup.c +++ b/block/bfq-cgroup.c @@ -593,12 +593,13 @@ struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd, */ entity = &bfqg->entity; for_each_entity(entity) { - bfqg = container_of(entity, struct bfq_group, entity); - if (bfqg != bfqd->root_group) { - parent = bfqg_parent(bfqg); + struct bfq_group *curr_bfqg = container_of(entity, + struct bfq_group, entity); + if (curr_bfqg != bfqd->root_group) { + parent = bfqg_parent(curr_bfqg); if (!parent) parent = bfqd->root_group; - bfq_group_set_parent(bfqg, parent); + bfq_group_set_parent(curr_bfqg, parent); } }