net: annotate accesses to sk->sk_incoming_cpu

This socket field can be read and written by concurrent cpus.

Use READ_ONCE() and WRITE_ONCE() annotations to document this,
and avoid some compiler 'optimizations'.

KCSAN reported :

BUG: KCSAN: data-race in tcp_v4_rcv / tcp_v4_rcv

write to 0xffff88812220763c of 4 bytes by interrupt on cpu 0:
 sk_incoming_cpu_update include/net/sock.h:953 [inline]
 tcp_v4_rcv+0x1b3c/0x1bb0 net/ipv4/tcp_ipv4.c:1934
 ip_protocol_deliver_rcu+0x4d/0x420 net/ipv4/ip_input.c:204
 ip_local_deliver_finish+0x110/0x140 net/ipv4/ip_input.c:231
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip_local_deliver+0x133/0x210 net/ipv4/ip_input.c:252
 dst_input include/net/dst.h:442 [inline]
 ip_rcv_finish+0x121/0x160 net/ipv4/ip_input.c:413
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip_rcv+0x18f/0x1a0 net/ipv4/ip_input.c:523
 __netif_receive_skb_one_core+0xa7/0xe0 net/core/dev.c:5010
 __netif_receive_skb+0x37/0xf0 net/core/dev.c:5124
 process_backlog+0x1d3/0x420 net/core/dev.c:5955
 napi_poll net/core/dev.c:6392 [inline]
 net_rx_action+0x3ae/0xa90 net/core/dev.c:6460
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1082
 do_softirq.part.0+0x6b/0x80 kernel/softirq.c:337
 do_softirq kernel/softirq.c:329 [inline]
 __local_bh_enable_ip+0x76/0x80 kernel/softirq.c:189

read to 0xffff88812220763c of 4 bytes by interrupt on cpu 1:
 sk_incoming_cpu_update include/net/sock.h:952 [inline]
 tcp_v4_rcv+0x181a/0x1bb0 net/ipv4/tcp_ipv4.c:1934
 ip_protocol_deliver_rcu+0x4d/0x420 net/ipv4/ip_input.c:204
 ip_local_deliver_finish+0x110/0x140 net/ipv4/ip_input.c:231
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip_local_deliver+0x133/0x210 net/ipv4/ip_input.c:252
 dst_input include/net/dst.h:442 [inline]
 ip_rcv_finish+0x121/0x160 net/ipv4/ip_input.c:413
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip_rcv+0x18f/0x1a0 net/ipv4/ip_input.c:523
 __netif_receive_skb_one_core+0xa7/0xe0 net/core/dev.c:5010
 __netif_receive_skb+0x37/0xf0 net/core/dev.c:5124
 process_backlog+0x1d3/0x420 net/core/dev.c:5955
 napi_poll net/core/dev.c:6392 [inline]
 net_rx_action+0x3ae/0xa90 net/core/dev.c:6460
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16 Comm: ksoftirqd/1 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -954,8 +954,8 @@ static inline void sk_incoming_cpu_update(struct sock *sk)
 {
 	int cpu = raw_smp_processor_id();
 
-	if (unlikely(sk->sk_incoming_cpu != cpu))
-		sk->sk_incoming_cpu = cpu;
+	if (unlikely(READ_ONCE(sk->sk_incoming_cpu) != cpu))
+		WRITE_ONCE(sk->sk_incoming_cpu, cpu);
 }
 
 static inline void sock_rps_record_flow_hash(__u32 hash)

net/core/sock.c

@@ -1127,7 +1127,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 		break;
 		}
 	case SO_INCOMING_CPU:
-		sk->sk_incoming_cpu = val;
+		WRITE_ONCE(sk->sk_incoming_cpu, val);
 		break;
 
 	case SO_CNX_ADVICE:
@@ -1476,7 +1476,7 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
 		break;
 
 	case SO_INCOMING_CPU:
-		v.val = sk->sk_incoming_cpu;
+		v.val = READ_ONCE(sk->sk_incoming_cpu);
 		break;
 
 	case SO_MEMINFO:

net/ipv4/inet_hashtables.c

@@ -240,7 +240,7 @@ static inline int compute_score(struct sock *sk, struct net *net,
 			return -1;
 
 		score = sk->sk_family == PF_INET ? 2 : 1;
-		if (sk->sk_incoming_cpu == raw_smp_processor_id())
+		if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())
 			score++;
 	}
 	return score;

net/ipv4/udp.c

@@ -388,7 +388,7 @@ static int compute_score(struct sock *sk, struct net *net,
 		return -1;
 	score += 4;
 
-	if (sk->sk_incoming_cpu == raw_smp_processor_id())
+	if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())
 		score++;
 	return score;
 }

net/ipv6/inet6_hashtables.c

@@ -105,7 +105,7 @@ static inline int compute_score(struct sock *sk, struct net *net,
 			return -1;
 
 		score = 1;
-		if (sk->sk_incoming_cpu == raw_smp_processor_id())
+		if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())
 			score++;
 	}
 	return score;

net/ipv6/udp.c

@@ -135,7 +135,7 @@ static int compute_score(struct sock *sk, struct net *net,
 		return -1;
 	score++;
 
-	if (sk->sk_incoming_cpu == raw_smp_processor_id())
+	if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())
 		score++;
 
 	return score;