sched: only update rq->clock while holding rq->lock

Vatsa noticed rq->clock going funny and tracked it down to an update_rq_clock()
outside a rq->lock section.

This is a problem because things like double_rq_lock() update the rq->clock
value for both rqs. Therefore disabling interrupts isn't strong enough.

Reported-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 1 insertions, 5 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 6f230596bd0c..c530b84c7f80 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4441,12 +4441,8 @@ need_resched_nonpreemptible:
         if (sched_feat(HRTICK))
                 hrtick_clear(rq);
 
-        /*
-         * Do the rq-clock update outside the rq lock:
-         */
-        local_irq_disable();
+        spin_lock_irq(&rq->lock);
         update_rq_clock(rq);
-        spin_lock(&rq->lock);
         clear_tsk_need_resched(prev);
 
         if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {