[RFC][PATCH 1/3] sched: Validate rq_clock*() serialization

[Peter Zijlstra <peterz@infradead.org>]

[-- Attachment #1: peterz-sched-rq_clock-locking.patch --]
[-- Type: text/plain, Size: 1270 bytes --]

rq->clock{,_task} are serialized by rq->lock, verify this.

One immediate fail is the usage in scale_rt_capability, so 'annotate'
that for now, there's more 'funny' there. Maybe change rq->lock into a
raw_seqlock_t?

(Only 32bit is affected)

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/fair.c  |    2 +-
 kernel/sched/sched.h |    7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5945,8 +5945,8 @@ static unsigned long scale_rt_capacity(i
 	 */
 	age_stamp = ACCESS_ONCE(rq->age_stamp);
 	avg = ACCESS_ONCE(rq->rt_avg);
+	delta = __rq_clock_broken(rq) - age_stamp;
 
-	delta = rq_clock(rq) - age_stamp;
 	if (unlikely(delta < 0))
 		delta = 0;
 
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -687,13 +687,20 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq
 #define cpu_curr(cpu)		(cpu_rq(cpu)->curr)
 #define raw_rq()		raw_cpu_ptr(&runqueues)
 
+static inline u64 __rq_clock_broken(struct rq *rq)
+{
+	return ACCESS_ONCE(rq->clock);
+}
+
 static inline u64 rq_clock(struct rq *rq)
 {
+	lockdep_assert_held(&rq->lock);
 	return rq->clock;
 }
 
 static inline u64 rq_clock_task(struct rq *rq)
 {
+	lockdep_assert_held(&rq->lock);
 	return rq->clock_task;
 }