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: Jan Beulich <[email protected]>
Signed-off-by: Wei Liu <[email protected]>
Reviewed-by: David Vrabel <[email protected]>
Cc: Ian Campbell <[email protected]>
Cc: Jason Luan <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index f3e591c611de..900da4b243ad 100644
--- 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 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);
 	}
 
@@ -1208,6 +1207,7 @@ 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;
 	}