sched: handle vruntime 64-bit overflow

Handle vruntime overflow by centering the key space around min_vruntime.

( otherwise we could overflow 64-bit vruntime in a few days with SCHED_IDLE
 tasks - or in a few years with nice +19. )

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 11 insertions, 4 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 86e5e8c5d101..895fef74d99a 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -124,11 +124,18 @@ set_leftmost(struct cfs_rq *cfs_rq, struct rb_node *leftmost)
         cfs_rq->rb_leftmost = leftmost;
         if (leftmost) {
                 se = rb_entry(leftmost, struct sched_entity, run_node);
-                cfs_rq->min_vruntime = max(se->vruntime,
-                                                cfs_rq->min_vruntime);
+                if ((se->vruntime > cfs_rq->min_vruntime) ||
+                    (cfs_rq->min_vruntime > (1ULL << 61) &&
+                     se->vruntime < (1ULL << 50)))
+                        cfs_rq->min_vruntime = se->vruntime;
         }
 }
 
+s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
+{
+        return se->fair_key - cfs_rq->min_vruntime;
+}
+
 /*
  * Enqueue an entity into the rb-tree:
  */
@@ -138,7 +145,7 @@ __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
         struct rb_node **link = &cfs_rq->tasks_timeline.rb_node;
         struct rb_node *parent = NULL;
         struct sched_entity *entry;
-        s64 key = se->fair_key;
+        s64 key = entity_key(cfs_rq, se);
         int leftmost = 1;
 
         /*
@@ -151,7 +158,7 @@ __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
                  * We dont care about collisions. Nodes with
                  * the same key stay together.
                  */
-                if (key - entry->fair_key < 0) {
+                if (key < entity_key(cfs_rq, entry)) {
                         link = &parent->rb_left;
                 } else {
                         link = &parent->rb_right;