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

[Kamal Mostafa]

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-3.8.y-queue branch of the 3.8.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-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.14.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 892a8b61569dee530010f9ff56bd09911a3d8350 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

[ Upstream commit 059dfa6a93b779516321e5112db9d7621b1367ba ]

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: Kamal Mostafa <kamal 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 1a28508..f2faa77 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 2ef5ec9..c63cbd0 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 f427455..d56fe61 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1427,9 +1427,8 @@ 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. */
@@ -1437,8 +1436,8 @@ 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);
 	}

@@ -1450,6 +1449,7 @@ 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