Use READ/WRITE_ONCE() for IP local_port_range.

Commit 227b60f5102cd added a seqlock to ensure that the low and high
port numbers were always updated together.
This is overkill because the two 16bit port numbers can be held in
a u32 and read/written in a single instruction.

More recently 91d0b78c5177f added support for finer per-socket limits.
The user-supplied value is 'high << 16 | low' but they are held
separately and the socket options protected by the socket lock.

Use a u32 containing 'high << 16 | low' for both the 'net' and 'sk'
fields and use READ_ONCE()/WRITE_ONCE() to ensure both values are
always updated together.

Change (the now trival) inet_get_local_port_range() to a static inline
to optimise the calling code.
(In particular avoiding returning integers by reference.)

Signed-off-by: David Laight <david.laight@aculab.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Acked-by: Mat Martineau <martineau@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/4e505d4198e946a8be03fb1b4c3072b0@AcuMS.aculab.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 9 insertions, 7 deletions

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 74db6d97cae1..aa86453f6b9b 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -234,10 +234,7 @@ struct inet_sock {
 	int			uc_index;
 	int			mc_index;
 	__be32			mc_addr;
-	struct {
-		__u16 lo;
-		__u16 hi;
-	}			local_port_range;
+	u32			local_port_range;	/* high << 16 | low */
 
 	struct ip_mc_socklist __rcu	*mc_list;
 	struct inet_cork_full	cork;
diff --git a/include/net/ip.h b/include/net/ip.h
index 1fc4c8d69e33..b31be912489a 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -349,7 +349,13 @@ static inline u64 snmp_fold_field64(void __percpu *mib, int offt, size_t syncp_o
 	} \
 }
 
-void inet_get_local_port_range(const struct net *net, int *low, int *high);
+static inline void inet_get_local_port_range(const struct net *net, int *low, int *high)
+{
+	u32 range = READ_ONCE(net->ipv4.ip_local_ports.range);
+
+	*low = range & 0xffff;
+	*high = range >> 16;
+}
 void inet_sk_get_local_port_range(const struct sock *sk, int *low, int *high);
 
 #ifdef CONFIG_SYSCTL
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index ea882964c71e..c356c458b340 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -19,8 +19,7 @@ struct hlist_head;
 struct fib_table;
 struct sock;
 struct local_ports {
-	seqlock_t	lock;
-	int		range[2];
+	u32		range;	/* high << 16 | low */
 	bool		warned;
 };