[PATCH] net: gre: complete lockless access to dev->needed_headroom

[Xiaochen Zou]

According to 4b397c06cb9 (net: tunnels: annotate lockless
accesses to dev->needed_headroom), we need to use lockless
access to protect dev->needed_headroom from data racing.
This patch complete the changes in ip(6)_gre.

More changes in other modules might be needed for completeness.

Signed-off-by: Xiaochen Zou <xzou017@xxxxxxx>
---
 net/ipv4/ip_gre.c  | 12 ++++++------
 net/ipv6/ip6_gre.c | 12 ++++++------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 5169c3c72cff..8c979c421d79 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -491,7 +491,7 @@ static void gre_fb_xmit(struct sk_buff *skb, struct net_device *dev,
 	key = &tun_info->key;
 	tunnel_hlen = gre_calc_hlen(key->tun_flags);
 
-	if (skb_cow_head(skb, dev->needed_headroom))
+	if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom)))
 		goto err_free_skb;
 
 	/* Push Tunnel header. */
@@ -541,7 +541,7 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct net_device *dev)
 	version = md->version;
 	tunnel_hlen = 8 + erspan_hdr_len(version);
 
-	if (skb_cow_head(skb, dev->needed_headroom))
+	if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom)))
 		goto err_free_skb;
 
 	if (gre_handle_offloads(skb, false))
@@ -653,7 +653,7 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
 		    skb_checksum_start(skb) < skb->data)
 			goto free_skb;
 	} else {
-		if (skb_cow_head(skb, dev->needed_headroom))
+		if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom)))
 			goto free_skb;
 
 		tnl_params = &tunnel->parms.iph;
@@ -689,7 +689,7 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
 	if (gre_handle_offloads(skb, false))
 		goto free_skb;
 
-	if (skb_cow_head(skb, dev->needed_headroom))
+	if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom)))
 		goto free_skb;
 
 	if (skb->len > dev->mtu + dev->hard_header_len) {
@@ -742,7 +742,7 @@ static netdev_tx_t gre_tap_xmit(struct sk_buff *skb,
 	if (gre_handle_offloads(skb, !!(tunnel->parms.o_flags & TUNNEL_CSUM)))
 		goto free_skb;
 
-	if (skb_cow_head(skb, dev->needed_headroom))
+	if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom)))
 		goto free_skb;
 
 	__gre_xmit(skb, dev, &tunnel->parms.iph, htons(ETH_P_TEB));
@@ -768,7 +768,7 @@ static void ipgre_link_update(struct net_device *dev, bool set_mtu)
 	if (dev->header_ops)
 		dev->hard_header_len += len;
 	else
-		dev->needed_headroom += len;
+		WRITE_ONCE(dev->needed_headroom, dev->needed_headroom + len);
 
 	if (set_mtu)
 		dev->mtu = max_t(int, dev->mtu - len, 68);
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 070d87abf7c0..8c060591641d 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -782,7 +782,7 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
 			(TUNNEL_CSUM | TUNNEL_KEY | TUNNEL_SEQ);
 		tun_hlen = gre_calc_hlen(flags);
 
-		if (skb_cow_head(skb, dev->needed_headroom ?: tun_hlen + tunnel->encap_hlen))
+		if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom) ?: tun_hlen + tunnel->encap_hlen))
 			return -ENOMEM;
 
 		gre_build_header(skb, tun_hlen,
@@ -792,7 +792,7 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
 						      : 0);
 
 	} else {
-		if (skb_cow_head(skb, dev->needed_headroom ?: tunnel->hlen))
+		if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom) ?: tunnel->hlen))
 			return -ENOMEM;
 
 		flags = tunnel->parms.o_flags;
@@ -976,7 +976,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 			truncate = true;
 	}
 
-	if (skb_cow_head(skb, dev->needed_headroom ?: t->hlen))
+	if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom) ?: t->hlen))
 		goto tx_err;
 
 	t->parms.o_flags &= ~TUNNEL_KEY;
@@ -1153,7 +1153,7 @@ static void ip6gre_tnl_link_config_route(struct ip6_tnl *t, int set_mtu,
 			if (t->dev->header_ops)
 				dev->hard_header_len = dst_len;
 			else
-				dev->needed_headroom = dst_len;
+				WRITE_ONCE(dev->needed_headroom, dst_len);
 
 			if (set_mtu) {
 				int mtu = rt->dst.dev->mtu - t_hlen;
@@ -1184,7 +1184,7 @@ static int ip6gre_calc_hlen(struct ip6_tnl *tunnel)
 	if (tunnel->dev->header_ops)
 		tunnel->dev->hard_header_len = LL_MAX_HEADER + t_hlen;
 	else
-		tunnel->dev->needed_headroom = LL_MAX_HEADER + t_hlen;
+		WRITE_ONCE(tunnel->dev->needed_headroom, LL_MAX_HEADER + t_hlen);
 
 	return t_hlen;
 }
@@ -1864,7 +1864,7 @@ static int ip6erspan_calc_hlen(struct ip6_tnl *tunnel)
 		       erspan_hdr_len(tunnel->parms.erspan_ver);
 
 	t_hlen = tunnel->hlen + sizeof(struct ipv6hdr);
-	tunnel->dev->needed_headroom = LL_MAX_HEADER + t_hlen;
+	WRITE_ONCE(tunnel->dev->needed_headroom, LL_MAX_HEADER + t_hlen);
 	return t_hlen;
 }
 
-- 
2.25.1