Re: [tip:sched/core] sched/core: Add debugging code to catch missing update_rq_clock() calls

[Peter Zijlstra]

On Tue, Jan 31, 2017 at 10:22:47AM -0700, Ross Zwisler wrote:
> On Tue, Jan 31, 2017 at 4:48 AM, Mike Galbraith <efa...@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);
        }