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, 1 insertions, 5 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index f61837ad336d..613c1c749677 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2014,21 +2014,17 @@ static void moved_group_fair(struct task_struct *p)
 }
 #endif
 
-unsigned int get_rr_interval_fair(struct task_struct *task)
+unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task)
 {
         struct sched_entity *se = &task->se;
-        unsigned long flags;
-        struct rq *rq;
         unsigned int rr_interval = 0;
 
         /*
          * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
          * idle runqueue:
          */
-        rq = task_rq_lock(task, &flags);
         if (rq->cfs.load.weight)
                 rr_interval = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));
-        task_rq_unlock(rq, &flags);
 
         return rr_interval;
 }