Merge branch 'for-3.12-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fixes from Tejun Heo:
 "Two late fixes for cgroup.

  One fixes descendant walk introduced during this rc1 cycle.  The other
  fixes a post 3.9 bug during task attach which can lead to hang.  Both
  fixes are critical and the fixes are relatively straight-forward"

* 'for-3.12-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: fix to break the while loop in cgroup_attach_task() correctly
  cgroup: fix cgroup post-order descendant walk of empty subtree

1 files changed, 6 insertions, 8 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2418b6e71a85..8bd9cfdc70d7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2039,7 +2039,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
 
                 /* @tsk either already exited or can't exit until the end */
                 if (tsk->flags & PF_EXITING)
-                        continue;
+                        goto next;
 
                 /* as per above, nr_threads may decrease, but not increase. */
                 BUG_ON(i >= group_size);
@@ -2047,7 +2047,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
                 ent.cgrp = task_cgroup_from_root(tsk, root);
                 /* nothing to do if this task is already in the cgroup */
                 if (ent.cgrp == cgrp)
-                        continue;
+                        goto next;
                 /*
                  * saying GFP_ATOMIC has no effect here because we did prealloc
                  * earlier, but it's good form to communicate our expectations.
@@ -2055,7 +2055,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
                 retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
                 BUG_ON(retval != 0);
                 i++;
-
+        next:
                 if (!threadgroup)
                         break;
         } while_each_thread(leader, tsk);
@@ -3188,11 +3188,9 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
 
         WARN_ON_ONCE(!rcu_read_lock_held());
 
-        /* if first iteration, visit the leftmost descendant */
-        if (!pos) {
-                next = css_leftmost_descendant(root);
-                return next != root ? next : NULL;
-        }
+        /* if first iteration, visit leftmost descendant which may be @root */
+        if (!pos)
+                return css_leftmost_descendant(root);
 
         /* if we visited @root, we're done */
         if (pos == root)