[PATCH v3 net-next 07/13] net-sysfs: convert dev->operstate reads to lockless ones

[Eric Dumazet <edumazet@google.com>]

operstate_show() can omit dev_base_lock acquisition only
to read dev->operstate.

Annotate accesses to dev->operstate.

Writers still acquire dev_base_lock for mutual exclusion.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/bridge/br_netlink.c |  3 ++-
 net/core/link_watch.c   |  4 ++--
 net/core/net-sysfs.c    |  4 +---
 net/core/rtnetlink.c    |  4 ++--
 net/hsr/hsr_device.c    | 10 +++++-----
 net/ipv6/addrconf.c     |  2 +-
 6 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 5ad4abfcb7ba3960bf69613ae7975180ae48854b..2cf4fc756263992eefe6a3580410766fea0c2c1f 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -455,7 +455,8 @@ static int br_fill_ifinfo(struct sk_buff *skb,
 			  u32 filter_mask, const struct net_device *dev,
 			  bool getlink)
 {
-	u8 operstate = netif_running(dev) ? dev->operstate : IF_OPER_DOWN;
+	u8 operstate = netif_running(dev) ? READ_ONCE(dev->operstate) :
+					    IF_OPER_DOWN;
 	struct nlattr *af = NULL;
 	struct net_bridge *br;
 	struct ifinfomsg *hdr;
diff --git a/net/core/link_watch.c b/net/core/link_watch.c
index 429571c258da7720baf387fef81081a56a655ef5..1b93e054c9a3cfcdd5d1251a9982d88a071abbaa 100644
--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -67,7 +67,7 @@ static void rfc2863_policy(struct net_device *dev)
 {
 	unsigned char operstate = default_operstate(dev);
 
-	if (operstate == dev->operstate)
+	if (operstate == READ_ONCE(dev->operstate))
 		return;
 
 	write_lock(&dev_base_lock);
@@ -87,7 +87,7 @@ static void rfc2863_policy(struct net_device *dev)
 		break;
 	}
 
-	dev->operstate = operstate;
+	WRITE_ONCE(dev->operstate, operstate);
 
 	write_unlock(&dev_base_lock);
 }
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 23ef2df549c3036a702f3be1dca1eda14ee5e76f..c5d164b8c6bfb53793f8422063c6281d6339b36e 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -325,11 +325,9 @@ static ssize_t operstate_show(struct device *dev,
 	const struct net_device *netdev = to_net_dev(dev);
 	unsigned char operstate;
 
-	read_lock(&dev_base_lock);
-	operstate = netdev->operstate;
+	operstate = READ_ONCE(netdev->operstate);
 	if (!netif_running(netdev))
 		operstate = IF_OPER_DOWN;
-	read_unlock(&dev_base_lock);
 
 	if (operstate >= ARRAY_SIZE(operstates))
 		return -EINVAL; /* should not happen */
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 8d95e0863534f80cecceb2dd4a7b2a16f7f4bca3..4e797326c88fe1e23ca66e82103176767fe5c32e 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -866,9 +866,9 @@ static void set_operstate(struct net_device *dev, unsigned char transition)
 		break;
 	}
 
-	if (dev->operstate != operstate) {
+	if (READ_ONCE(dev->operstate) != operstate) {
 		write_lock(&dev_base_lock);
-		dev->operstate = operstate;
+		WRITE_ONCE(dev->operstate, operstate);
 		write_unlock(&dev_base_lock);
 		netdev_state_change(dev);
 	}
diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
index 9d71b66183daf94e19945d75cfb5c33df6ce346c..be0e43f46556e028e675147e63c6b787aa72e894 100644
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -31,8 +31,8 @@ static bool is_slave_up(struct net_device *dev)
 static void __hsr_set_operstate(struct net_device *dev, int transition)
 {
 	write_lock(&dev_base_lock);
-	if (dev->operstate != transition) {
-		dev->operstate = transition;
+	if (READ_ONCE(dev->operstate) != transition) {
+		WRITE_ONCE(dev->operstate, transition);
 		write_unlock(&dev_base_lock);
 		netdev_state_change(dev);
 	} else {
@@ -78,14 +78,14 @@ static void hsr_check_announce(struct net_device *hsr_dev,
 
 	hsr = netdev_priv(hsr_dev);
 
-	if (hsr_dev->operstate == IF_OPER_UP && old_operstate != IF_OPER_UP) {
+	if (READ_ONCE(hsr_dev->operstate) == IF_OPER_UP && old_operstate != IF_OPER_UP) {
 		/* Went up */
 		hsr->announce_count = 0;
 		mod_timer(&hsr->announce_timer,
 			  jiffies + msecs_to_jiffies(HSR_ANNOUNCE_INTERVAL));
 	}
 
-	if (hsr_dev->operstate != IF_OPER_UP && old_operstate == IF_OPER_UP)
+	if (READ_ONCE(hsr_dev->operstate) != IF_OPER_UP && old_operstate == IF_OPER_UP)
 		/* Went down */
 		del_timer(&hsr->announce_timer);
 }
@@ -100,7 +100,7 @@ void hsr_check_carrier_and_operstate(struct hsr_priv *hsr)
 	/* netif_stacked_transfer_operstate() cannot be used here since
 	 * it doesn't set IF_OPER_LOWERLAYERDOWN (?)
 	 */
-	old_operstate = master->dev->operstate;
+	old_operstate = READ_ONCE(master->dev->operstate);
 	has_carrier = hsr_check_carrier(master);
 	hsr_set_operstate(master, has_carrier);
 	hsr_check_announce(master->dev, old_operstate);
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d63f5d063f073cb53f52e187efdbd09b8f78d622..1122c9ef09f6210fc373d9678a9da1ec1a3e78fa 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5998,7 +5998,7 @@ static int inet6_fill_ifinfo(struct sk_buff *skb, struct inet6_dev *idev,
 	    (dev->ifindex != dev_get_iflink(dev) &&
 	     nla_put_u32(skb, IFLA_LINK, dev_get_iflink(dev))) ||
 	    nla_put_u8(skb, IFLA_OPERSTATE,
-		       netif_running(dev) ? dev->operstate : IF_OPER_DOWN))
+		       netif_running(dev) ? READ_ONCE(dev->operstate) : IF_OPER_DOWN))
 		goto nla_put_failure;
 	protoinfo = nla_nest_start_noflag(skb, IFLA_PROTINFO);
 	if (!protoinfo)
-- 
2.43.0.687.g38aa6559b0-goog