Quoting Paul Menage (menage@xxxxxxxxxx):
> cgroup: Fix root_count when mount fails due to busy subsystem
>
> root_count was being incremented in cgroup_get_sb() after all error
> checking was complete, but decremented in cgroup_kill_sb(), which can
> be called on a superblock that we gave up on due to an error. This
> patch changes cgroup_kill_sb() to only decrement root_count if the
> root was previously linked into the list of roots.
>
> Signed-off-by: Paul Menage <menage@xxxxxxxxxx>
Tested-by: Serge Hallyn <serue@xxxxxxxxxx>
thanks,
-serge
>
> ---
>
> I was actually surprised to find that list_del() doesn't crash when
> run on an unattached list_head structure.
>
> kernel/cgroup.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index adcd0bb..9ce27e8 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1115,8 +1115,10 @@ static void cgroup_kill_sb(struct super_block *sb) {
> }
> write_unlock(&css_set_lock);
>
> - list_del(&root->root_list);
> - root_count--;
> + if (!list_empty(&root->root_list)) {
> + list_del(&root->root_list);
> + root_count--;
> + }
>
> mutex_unlock(&cgroup_mutex);
>
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