[PATCH 3.12 05/19] xen-netback: use jiffies_64 value to calculate credit timeout

Greg Kroah-Hartman
2013-11-18T18:37:58Z

From: Wei Liu <wei.liu2@citrix.com>

[ 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@suse.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Jason Luan <jianhai.luan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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(-)

--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -163,6 +163,7 @@ 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;
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -312,8 +312,7 @@ struct xenvif *xenvif_alloc(struct devic
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;
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1185,9 +1185,8 @@ 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. */
@@ -1195,8 +1194,8 @@ static bool tx_credit_exceeded(struct xe
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);
}

@@ -1208,6 +1207,7 @@ static bool tx_credit_exceeded(struct xe
tx_credit_callback;
mod_timer(&vif->credit_timeout,
next_credit);
+ vif->credit_window_start = next_credit;

return true;
}