linux-kernel - [PATCH tip/core/rcu 2/2] rcu: make task_subsys_state() RCU-lockdep checks handle boot-time use

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Message-Id: <1267311188-16603-2-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Sat, 27 Feb 2010 14:53:08 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 2/2] 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@...e.hu>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 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());
 }
 
-- 
1.6.6

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