netdev - Re: [PATCH 4/8] ethoc: prevent overflow of rx counter

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Date:	Wed, 24 Nov 2010 18:34:27 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jonas Bonn <jonas@...thpole.se>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 4/8] ethoc: prevent overflow of rx counter

Le mercredi 24 novembre 2010 à 14:40 +0100, Jonas Bonn a écrit :
> Rewind cur_rx to prevent it from overflowing.
> 
> Signed-off-by: Jonas Bonn <jonas@...thpole.se>
> ---
>  drivers/net/ethoc.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/ethoc.c b/drivers/net/ethoc.c
> index 53c03f2..7d1b5d8 100644
> --- a/drivers/net/ethoc.c
> +++ b/drivers/net/ethoc.c
> @@ -408,6 +408,9 @@ static int ethoc_rx(struct net_device *dev, int limit)
>  	struct ethoc *priv = netdev_priv(dev);
>  	int count;
>  
> +	/* Prevent overflow of priv->cur_rx by rewinding it */	
> +	priv->cur_rx = priv->cur_rx % priv->num_rx;
> +
>  	for (count = 0; count < limit; ++count) {
>  		unsigned int entry;
>  		struct ethoc_bd bd;


Hmm... please try following code instead (no divides)

diff --git a/drivers/net/ethoc.c b/drivers/net/ethoc.c
index c5a2fe0..591b698 100644
--- a/drivers/net/ethoc.c
+++ b/drivers/net/ethoc.c
@@ -413,7 +413,7 @@ static int ethoc_rx(struct net_device *dev, int limit)
 		unsigned int entry;
 		struct ethoc_bd bd;
 
-		entry = priv->num_tx + (priv->cur_rx % priv->num_rx);
+		entry = priv->num_tx + priv->cur_rx;
 		ethoc_read_bd(priv, entry, &bd);
 		if (bd.stat & RX_BD_EMPTY)
 			break;
@@ -446,7 +446,8 @@ static int ethoc_rx(struct net_device *dev, int limit)
 		bd.stat &= ~RX_BD_STATS;
 		bd.stat |=  RX_BD_EMPTY;
 		ethoc_write_bd(priv, entry, &bd);
-		priv->cur_rx++;
+		if (++priv->cur_rx == priv->num_rx)
+			priv->cur_rx = 0;
 	}
 
 	return count;


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