[3.5.y.z extended stable] Patch "xen-netback: use jiffies_64 value to calculate credit timeout" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    xen-netback: use jiffies_64 value to calculate credit timeout

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 777f2852b6585872fa8e9f5715f619a59506e764 Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2 at citrix.com>
Date: Mon, 28 Oct 2013 12:07:57 +0000
Subject: xen-netback: use jiffies_64 value to calculate credit timeout

commit 059dfa6a93b779516321e5112db9d7621b1367ba upstream.

time_after_eq() only works if the delta is < MAX_ULONG/2.

For a 32bit Dom0, if netfront sends packets at a very low rate, the time
between subsequent calls to tx_credit_exceeded() may exceed MAX_ULONG/2
and the test for timer_after_eq() will be incorrect. Credit will not be
replenished and the guest may become unable to send packets (e.g., if
prior to the long gap, all credit was exhausted).

Use jiffies_64 variant to mitigate this problem for 32bit Dom0.

Suggested-by: Jan Beulich <jbeulich at suse.com>
Signed-off-by: Wei Liu <wei.liu2 at citrix.com>
Reviewed-by: David Vrabel <david.vrabel at citrix.com>
Cc: Ian Campbell <ian.campbell at citrix.com>
Cc: Jason Luan <jianhai.luan at oracle.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/net/xen-netback/common.h    |  1 +
 drivers/net/xen-netback/interface.c |  3 +--
 drivers/net/xen-netback/netback.c   | 10 +++++-----
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 9d7f172..093bf0a 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -88,6 +88,7 @@ struct xenvif {
 	unsigned long   credit_usec;
 	unsigned long   remaining_credit;
 	struct timer_list credit_timeout;
+	u64 credit_window_start;

 	/* Statistics */
 	unsigned long rx_gso_checksum_fixup;
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 221f426..cfaaf68 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -273,8 +273,7 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
 	vif->credit_bytes = vif->remaining_credit = ~0UL;
 	vif->credit_usec  = 0UL;
 	init_timer(&vif->credit_timeout);
-	/* Initialize 'expires' now: it's used to track the credit window. */
-	vif->credit_timeout.expires = jiffies;
+	vif->credit_window_start = get_jiffies_64();

 	dev->netdev_ops	= &xenvif_netdev_ops;
 	dev->hw_features = NETIF_F_SG | NETIF_F_IP_CSUM | NETIF_F_TSO;
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 228607b..3d0f22a 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1364,9 +1364,8 @@ out:

 static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
 {
-	unsigned long now = jiffies;
-	unsigned long next_credit =
-		vif->credit_timeout.expires +
+	u64 now = get_jiffies_64();
+	u64 next_credit = vif->credit_window_start +
 		msecs_to_jiffies(vif->credit_usec / 1000);

 	/* Timer could already be pending in rare cases. */
@@ -1374,8 +1373,8 @@ static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
 		return true;

 	/* Passed the point where we can replenish credit? */
-	if (time_after_eq(now, next_credit)) {
-		vif->credit_timeout.expires = now;
+	if (time_after_eq64(now, next_credit)) {
+		vif->credit_window_start = now;
 		tx_add_credit(vif);
 	}

@@ -1387,6 +1386,7 @@ static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
 			tx_credit_callback;
 		mod_timer(&vif->credit_timeout,
 			  next_credit);
+		vif->credit_window_start = next_credit;

 		return true;
 	}
--
1.8.3.2