From: Herbert Xu <herbert.xu@redhat.com>
Subject: [RHEL5.1 PATCH] [XEN] netfront: Better fix for netfront_tx_slot_available().
Date: Wed, 11 Apr 2007 16:33:43 +1000
Bugzilla: 224558
Message-Id: <20070411063343.GA17151@gondor.apana.org.au>
Changelog: [XEN] Better fix for netfront_tx_slot_available().


Hi:

RHEL5.1 BZ 224558

This is an upstream patch which fixes an accounting error in determining
whether enough resources are available for transmission of network packets.
As a direct result this can cause the frontend network driver to BUG which
brings down the guest OS.

# HG changeset patch
# User kfraser@localhost.localdomain
# Node ID e19f9d6a2ff594c948b66c7dc43dd70fecab1d3f
# Parent  fec1a697558853ffc61e1d8047a5dc2fa965e6a8
netfront: Better fix for netfront_tx_slot_available().
Signed-off-by: Keir Fraser <keir@xensource.com>

--- linux-2.6.18.noarch/drivers/xen/netfront/netfront.c.orig	2007-04-11 15:33:06.000000000 +1000
+++ linux-2.6.18.noarch/drivers/xen/netfront/netfront.c	2007-04-11 16:18:47.000000000 +1000
@@ -575,7 +575,8 @@
 
 static inline int netfront_tx_slot_available(struct netfront_info *np)
 {
-	return RING_FREE_REQUESTS(&np->tx) >= MAX_SKB_FRAGS + 2;
+	return ((np->tx.req_prod_pvt - np->tx.rsp_cons) <
+		(TX_MAX_TARGET - MAX_SKB_FRAGS - 2));
 }
 
 static inline void network_maybe_wake_tx(struct net_device *dev)

Cheers,
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Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
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