[PATCH 1/6] cgroup: subsys->attach_task() should be called after migration

[Tejun Heo]

cgroup_attach_task() calls subsys->attach_task() after
cgroup_task_migrate(); however, cgroup_attach_proc() calls it before
migration.  This actually affects some of the users.  Update
cgroup_attach_proc() such that ->attach_task() is called after
migration.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Paul Menage <paul@xxxxxxxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
 kernel/cgroup.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1d2b6ce..a606fa2 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2135,14 +2135,16 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 		oldcgrp = task_cgroup_from_root(tsk, root);
 		if (cgrp == oldcgrp)
 			continue;
+
+		/* 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);
+
 		/* 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);
 	}
 	/* nothing is sensitive to fork() after this point. */
 
-- 
1.7.6

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