sched/core: Add WARNING for multiple update_rq_clock() calls

Now that we have no missing calls, add a warning to find multiple
calls.

By having only a single update_rq_clock() call per rq-lock section,
the section appears 'atomic' wrt time.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 10 insertions, 0 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3b31fc05a0f1..1bd15d0d0307 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -233,8 +233,11 @@ void update_rq_clock(struct rq *rq)
                 return;
 
 #ifdef CONFIG_SCHED_DEBUG
+        if (sched_feat(WARN_DOUBLE_CLOCK))
+                SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
         rq->clock_update_flags |= RQCF_UPDATED;
 #endif
+
         delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
         if (delta < 0)
                 return;
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 1b3c8189b286..11192e0cb122 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -56,6 +56,13 @@ SCHED_FEAT(TTWU_QUEUE, true)
  */
 SCHED_FEAT(SIS_AVG_CPU, false)
 
+/*
+ * Issue a WARN when we do multiple update_rq_clock() calls
+ * in a single rq->lock section. Default disabled because the
+ * annotations are not complete.
+ */
+SCHED_FEAT(WARN_DOUBLE_CLOCK, false)
+
 #ifdef HAVE_RT_PUSH_IPI
 /*
  * In order to avoid a thundering herd attack of CPUs that are