[tip:core/rcu] rcu: Make task_subsys_state() RCU-lockdep checks handle boot-time use

["tip-bot for Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Commit-ID:  1883c79a57a5fe25309007590cccb1b2782c41b2
Gitweb:     http://git.kernel.org/tip/1883c79a57a5fe25309007590cccb1b2782c41b2
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Sat, 27 Feb 2010 14:53:08 -0800
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Sun, 28 Feb 2010 09:17:42 +0100

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>
---
 include/linux/cgroup.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c9bbcb2..a73e1ce 100644
--- 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());
 }