-
Li Zefan authored
We've converted cgroup to kernfs so cgroup won't be intertwined with vfs objects and locking, but there are dark areas. Run two instances of this script concurrently: for ((; ;)) { mount -t cgroup -o cpuacct xxx /cgroup umount /cgroup } After a while, I saw two mount processes were stuck at retrying, because they were waiting for a subsystem to become free, but the root associated with this subsystem never got freed. This can happen, if thread A is in the process of killing superblock but hasn't called percpu_ref_kill(), and at this time thread B is mounting the same cgroup root and finds the root in the root list and performs percpu_ref_try_get(). To fix this, we try to increase both the refcnt of the superblock and the percpu refcnt of cgroup root. v2: - we should try to get both the superblock refcnt and cgroup_root refcnt, because cgroup_root may have no superblock assosiated with it. - adjust/add comments. tj: Updated comments. Renamed @sb to @pinned_sb. Cc: <stable@vger.kernel.org> # 3.15 Signed-off-by:
Li Zefan <lizefan@huawei.com> Signed-off-by:
Tejun Heo <tj@kernel.org>
3a32bd72