cfq-iosched: fix possible problem with jiffies wraparound

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>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e7f9e4e3a270..ae14cbaf9d0e 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;