Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage

From: "Paul E. McKenney" <[email-masked]>
Date: Wed, 21 Apr 2010 14:48:48 -0700

On Wed, Apr 21, 2010 at 02:35:43PM -0700, Paul E. McKenney wrote:
> On Tue, Apr 20, 2010 at 11:38:28AM -0400, Miles Lane wrote:
> > Excellent.  Here are the results on my machine.  .config appended.
> 
> First, thank you very much for testing this, Miles!

And as Tetsuo Handa pointed out privately, my patch was way broken.

Here is an updated version.

							Thanx, Paul

commit b15e561ed91b7a366c3cc635026f3b9ce6483070
Author: Paul E. McKenney <[email-masked]>
Date:   Wed Apr 21 14:04:56 2010 -0700

    sched: protect __sched_setscheduler() access to cgroups
    
    A given task's cgroups structures must remain while that task is running
    due to reference counting, so this is presumably a false positive.
    Updated to reflect feedback from Tetsuo Handa.
    
    Signed-off-by: Paul E. McKenney <[email-masked]>

diff --git a/kernel/sched.c b/kernel/sched.c
index 14c44ec..f425a2b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4575,9 +4575,13 @@ recheck:
 		 * Do not allow realtime tasks into groups that have no runtime
 		 * assigned.
 		 */
+		rcu_read_lock();
 		if (rt_bandwidth_enabled() && rt_policy(policy) &&
-				task_group(p)->rt_bandwidth.rt_runtime == 0)
+				task_group(p)->rt_bandwidth.rt_runtime == 0) {
+			rcu_read_unlock();
 			return -EPERM;
+		}
+		rcu_read_unlock();
 #endif
 
 		retval = security_task_setscheduler(p, policy, param);