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 <[email protected]>
Tested-by: Serge Hallyn <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 492215d67fa5c3f153f6b1de42416ec4a1653298..5a54ff42874ee916997139c859b8cfda725b9a33 100644 (file)
--- 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);