[net,V3] 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 <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>
---
 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(-)

On 2013-10-28 20:07, Wei Liu wrote:
> 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>
> ---
>   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 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..459935a 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -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;
>   	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 f3e591c..900da4b 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;
>   	}

This patch looks good, thanks Wei.

Thanks
Annie
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From: Wei Liu <wei.liu2@citrix.com>
Date: Mon, 28 Oct 2013 12:07:57 +0000

> 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>

Applied and queued up for -stable, thanks.
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