[PATCH tip/core/urgent 3/3] sched: protect __sched_setscheduler() access to cgroups

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

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 <paulmck@linux.vnet.ibm.com>
---
 kernel/sched.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

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);
-- 
1.7.0