From: Corrado Zoccolo <czoccolo@gmail.com>
Date: Mon, 5 Oct 2009 06:49:23 +0000 (+0200)
Subject: cfq-iosched: fix possible problem with jiffies wraparound
X-Git-Tag: v2.6.32-rc5~26^2~14
X-Git-Url: http://ftp.safe.ca/?p=safe%2Fjmp%2Flinux-2.6;a=commitdiff_plain;h=48e025e63ac908ed6ec5394a294f4ecd510a7476

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>
---

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e7f9e4e..ae14cba 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;