[PATCH][BUGFIX] cgroups: fix ordering of calls in cgroup_attach_proc

[Ben Blum <bblum@andrew.cmu.edu>]

Fix ordering of cgroup_task_migrate and attach_task in cgroup_attach_proc.

Signed-off-by: Ben Blum <bblum@andrew.cmu.edu>

---
 kernel/cgroup.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff -u a/kernel/cgroup.c b/kernel/cgroup.c
--- a/kernel/cgroup.c	2011-08-15 19:05:37.308401219 -0400
+++ b/kernel/cgroup.c	2011-08-15 19:07:47.376775142 -0400
@@ -2132,14 +2132,17 @@
 		oldcgrp = task_cgroup_from_root(tsk, root);
 		if (cgrp == oldcgrp)
 			continue;
-		/* attach each task to each subsystem */
-		for_each_subsys(root, ss) {
-			if (ss->attach_task)
-				ss->attach_task(cgrp, tsk);
-		}
 		/* if the thread is PF_EXITING, it can just get skipped. */
 		retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true);
-		BUG_ON(retval != 0 && retval != -ESRCH);
+		if (retval == 0) {
+			/* attach each task to each subsystem */
+			for_each_subsys(root, ss) {
+				if (ss->attach_task)
+					ss->attach_task(cgrp, tsk);
+			}
+		} else {
+			BUG_ON(retval != -ESRCH);
+		}
 	}
 	/* nothing is sensitive to fork() after this point. */