Commit 059dfa6a authored by Wei Liu's avatar Wei Liu Committed by David S. Miller
Browse files

xen-netback: use jiffies_64 value to calculate credit timeout

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: default avatarJan Beulich <>
Signed-off-by: default avatarWei Liu <>
Reviewed-by: default avatarDavid Vrabel <>
Cc: Ian Campbell <>
Cc: Jason Luan <>
Signed-off-by: default avatarDavid S. Miller <>
parent 262e827f
......@@ -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;
......@@ -312,8 +312,7 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
vif->credit_bytes = vif->remaining_credit = ~0UL;
vif->credit_usec = 0UL;
/* 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;
......@@ -1185,9 +1185,8 @@ static int checksum_setup(struct xenvif *vif, struct sk_buff *skb)
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 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;
......@@ -1208,6 +1207,7 @@ static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
vif->credit_window_start = next_credit;
return true;
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