netdev - Re: br_forward.c - rcu dereference warning

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Message-ID: <20100727112630.5a5ce84b@nehalam>
Date:	Tue, 27 Jul 2010 11:26:30 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Johannes Berg <johannes@...solutions.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: br_forward.c - rcu dereference warning

I think this is needed (untested)...
-----
Subject: bridge: add rcu_read_lock on transmit

Long ago, when bridge was converted to RCU, rcu lock was equivalent
to having preempt disabled. RCU has changed a lot since then and
bridge code was still assuming the since transmit was called with
bottom half disabled, it was RCU safe.

Signed-off-by: Stephen Hemminger <shemminger@...tta.com>


---
 net/bridge/br_device.c   |    4 +++-
 net/bridge/br_fdb.c      |    2 +-
 net/bridge/br_input.c    |    7 +++----
 net/bridge/br_stp_bpdu.c |    2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)

--- a/net/bridge/br_device.c	2010-07-27 08:57:43.169399349 -0700
+++ b/net/bridge/br_device.c	2010-07-27 11:18:51.677053426 -0700
@@ -22,7 +22,7 @@
 #include <asm/uaccess.h>
 #include "br_private.h"
 
-/* net device transmit always called with no BH (preempt_disabled) */
+/* net device transmit always called with no BH disabled */
 netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct net_bridge *br = netdev_priv(dev);
@@ -48,6 +48,7 @@ netdev_tx_t br_dev_xmit(struct sk_buff *
 	skb_reset_mac_header(skb);
 	skb_pull(skb, ETH_HLEN);
 
+	rcu_read_lock();
 	if (is_multicast_ether_addr(dest)) {
 		if (unlikely(netpoll_tx_running(dev))) {
 			br_flood_deliver(br, skb);
@@ -67,6 +68,7 @@ netdev_tx_t br_dev_xmit(struct sk_buff *
 		br_flood_deliver(br, skb);
 
 out:
+	rcu_read_unlock();
 	return NETDEV_TX_OK;
 }
 
--- a/net/bridge/br_fdb.c	2010-07-27 11:18:30.815320981 -0700
+++ b/net/bridge/br_fdb.c	2010-07-27 11:18:59.597710975 -0700
@@ -214,7 +214,7 @@ void br_fdb_delete_by_port(struct net_br
 	spin_unlock_bh(&br->hash_lock);
 }
 
-/* No locking or refcounting, assumes caller has no preempt (rcu_read_lock) */
+/* No locking or refcounting, assumes caller has rcu_read_lock */
 struct net_bridge_fdb_entry *__br_fdb_get(struct net_bridge *br,
 					  const unsigned char *addr)
 {
--- a/net/bridge/br_input.c	2010-07-27 11:19:05.266181492 -0700
+++ b/net/bridge/br_input.c	2010-07-27 11:19:29.148163149 -0700
@@ -39,7 +39,7 @@ static int br_pass_frame_up(struct sk_bu
 		       netif_receive_skb);
 }
 
-/* note: already called with rcu_read_lock (preempt_disabled) */
+/* note: already called with rcu_read_lock */
 int br_handle_frame_finish(struct sk_buff *skb)
 {
 	const unsigned char *dest = eth_hdr(skb)->h_dest;
@@ -110,7 +110,7 @@ drop:
 	goto out;
 }
 
-/* note: already called with rcu_read_lock (preempt_disabled) */
+/* note: already called with rcu_read_lock */
 static int br_handle_local_finish(struct sk_buff *skb)
 {
 	struct net_bridge_port *p = br_port_get_rcu(skb->dev);
@@ -133,8 +133,7 @@ static inline int is_link_local(const un
 
 /*
  * Return NULL if skb is handled
- * note: already called with rcu_read_lock (preempt_disabled) from
- * netif_receive_skb
+ * note: already called with rcu_read_lock from netif_receive_skb
  */
 struct sk_buff *br_handle_frame(struct sk_buff *skb)
 {
--- a/net/bridge/br_stp_bpdu.c	2010-07-27 11:19:34.092573294 -0700
+++ b/net/bridge/br_stp_bpdu.c	2010-07-27 11:19:40.725123403 -0700
@@ -131,7 +131,7 @@ void br_send_tcn_bpdu(struct net_bridge_
 /*
  * Called from llc.
  *
- * NO locks, but rcu_read_lock (preempt_disabled)
+ * NO locks, but rcu_read_lock
  */
 void br_stp_rcv(const struct stp_proto *proto, struct sk_buff *skb,
 		struct net_device *dev)
--
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