cfq: fix possible problem with jiffies wraparound

Corrado Zoccolo
2009-10-04T17:10:39Z

The RR service tree is indexed by a key that is relative to current jiffies.
This can cause problems on jiffies wraparound.

The patch fixes it using time_before comparison, and changing
the add_front path to use a relative number, too.

Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
---
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 576e92d..495b16d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -512,8 +512,11 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
rb_key += cfqq->slice_resid;
cfqq->slice_resid = 0;
- } else
- rb_key = 0;
+ } else {
+ rb_key = -HZ;
+ __cfqq = cfq_rb_first(&cfqd->service_tree);
+ rb_key += __cfqq ? __cfqq->rb_key : jiffies;
+ }

if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
/*
@@ -547,7 +550,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
n = &(*p)->rb_left;
else if (cfq_class_idle(cfqq) > cfq_class_idle(__cfqq))
n = &(*p)->rb_right;
- else if (rb_key < __cfqq->rb_key)
+ else if (time_before(rb_key, __cfqq->rb_key))
n = &(*p)->rb_left;
else
n = &(*p)->rb_right;