[Xen-devel] [PATCH net] xen-netback: use jiffies_64 value to calculate credit timeout

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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@xxxxxxxx>
Suggested-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Jason Luan <jianhai.luan@xxxxxxxxxx>
---
 drivers/net/xen-netback/common.h    |    1 +
 drivers/net/xen-netback/interface.c |    4 ++--
 drivers/net/xen-netback/netback.c   |   13 ++++++-------
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 5715318..400fea1 100644
--- 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;
diff --git a/drivers/net/xen-netback/interface.c 
b/drivers/net/xen-netback/interface.c
index 01bb854..8c45b63 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -312,8 +312,8 @@ 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;
+       /* credit window is tracked in credit_window_start */
+       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 f3e591c..1bc0688 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1185,18 +1185,17 @@ out:
 
 static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
 {
-       unsigned long now = jiffies;
-       unsigned long next_credit =
-               vif->credit_timeout.expires +
-               msecs_to_jiffies(vif->credit_usec / 1000);
+       u64 now = get_jiffies_64();
+       u64 next_credit = vif->credit_window_start +
+               (u64)msecs_to_jiffies(vif->credit_usec / 1000);
 
        /* Timer could already be pending in rare cases. */
        if (timer_pending(&vif->credit_timeout))
                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_timeout.expires = (unsigned long)now;
                tx_add_credit(vif);
        }
 
@@ -1207,7 +1206,7 @@ static bool tx_credit_exceeded(struct xenvif *vif, 
unsigned size)
                vif->credit_timeout.function =
                        tx_credit_callback;
                mod_timer(&vif->credit_timeout,
-                         next_credit);
+                         (unsigned long)next_credit);
 
                return true;
        }
-- 
1.7.10.4


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