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SubjectRe: [tip:sched/core] sched/core: Add debugging code to catch missing update_rq_clock() calls
On Tue, Jan 31, 2017 at 10:22:47AM -0700, Ross Zwisler wrote:
> On Tue, Jan 31, 2017 at 4:48 AM, Mike Galbraith <efault@gmx.de> wrote:
> > On Tue, 2017-01-31 at 16:30 +0530, Sachin Sant wrote:


Could some of you test this? It seems to cure things in my (very)
limited testing.

---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 96e4ccc..b773821 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5609,7 +5609,7 @@ static void migrate_tasks(struct rq *dead_rq)
{
struct rq *rq = dead_rq;
struct task_struct *next, *stop = rq->stop;
- struct rq_flags rf, old_rf;
+ struct rq_flags rf;
int dest_cpu;

/*
@@ -5628,7 +5628,9 @@ static void migrate_tasks(struct rq *dead_rq)
* class method both need to have an up-to-date
* value of rq->clock[_task]
*/
+ rq_pin_lock(rq, &rf);
update_rq_clock(rq);
+ rq_unpin_lock(rq, &rf);

for (;;) {
/*
@@ -5641,7 +5643,7 @@ static void migrate_tasks(struct rq *dead_rq)
/*
* pick_next_task assumes pinned rq->lock.
*/
- rq_pin_lock(rq, &rf);
+ rq_repin_lock(rq, &rf);
next = pick_next_task(rq, &fake_task, &rf);
BUG_ON(!next);
next->sched_class->put_prev_task(rq, next);
@@ -5670,13 +5672,6 @@ static void migrate_tasks(struct rq *dead_rq)
continue;
}

- /*
- * __migrate_task() may return with a different
- * rq->lock held and a new cookie in 'rf', but we need
- * to preserve rf::clock_update_flags for 'dead_rq'.
- */
- old_rf = rf;
-
/* Find suitable destination for @next, with force if needed. */
dest_cpu = select_fallback_rq(dead_rq->cpu, next);

@@ -5685,7 +5680,6 @@ static void migrate_tasks(struct rq *dead_rq)
raw_spin_unlock(&rq->lock);
rq = dead_rq;
raw_spin_lock(&rq->lock);
- rf = old_rf;
}
raw_spin_unlock(&next->pi_lock);
}
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