sched: Protect sched_rr_get_param() access to task->sched_class

sched_rr_get_param calls
task->sched_class->get_rr_interval(task) without protection
against a concurrent sched_setscheduler() call which modifies
task->sched_class.

Serialize the access with task_rq_lock(task) and hand the rq
pointer into get_rr_interval() as it's needed at least in the
sched_fair implementation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <alpine.LFD.2.00.0912090930120.3089@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 89115ec7d43f..9b2402725088 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1111,7 +1111,8 @@ struct sched_class {
         void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
                              int oldprio, int running);
 
-        unsigned int (*get_rr_interval) (struct task_struct *task);
+        unsigned int (*get_rr_interval) (struct rq *rq,
+                                         struct task_struct *task);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
         void (*moved_group) (struct task_struct *p);