rcu: Make task_subsys_state() RCU-lockdep checks handle boot-time use

It is apparently legal to invoke task_subsys_state() without RCU
protection during early boot time.  After all, there are no
concurrent tasks, so there can be no grace periods completing
concurrently.

But this does need an Acked-by from the cgroups folks.

Located-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1267311188-16603-2-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c9bbcb2a75aecbacdb1463cf08a2b0a26d0f264b..a73e1ced09b863d675aa2cfca6e4540d4f471a2f 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -489,6 +489,7 @@ static inline struct cgroup_subsys_state *task_subsys_state(
 {
        return rcu_dereference_check(task->cgroups->subsys[subsys_id],
                                     rcu_read_lock_held() ||
+                                    !rcu_scheduler_active ||
                                     cgroup_lock_is_held());
 }