sock: annotate data-races around prot->memory_pressure

*prot->memory_pressure is read/writen locklessly, we need
to add proper annotations.

A recent commit added a new race, it is time to audit all accesses.

Fixes: 2d0c88e ("sock: Fix misuse of sk_under_memory_pressure()")
Fixes: 4d93df0 ("[SCTP]: Rewrite of sctp buffer management code")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Abel Wu <wuyun.abel@bytedance.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Link: https://lore.kernel.org/r/20230818015132.2699348-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

include/net/sock.h

@@ -1323,6 +1323,7 @@ struct proto {
 	/*
 	 * Pressure flag: try to collapse.
 	 * Technical note: it is used by multiple contexts non atomically.
+	 * Make sure to use READ_ONCE()/WRITE_ONCE() for all reads/writes.
 	 * All the __sk_mem_schedule() is of this nature: accounting
 	 * is strict, actions are advisory and have some latency.
 	 */
@@ -1423,7 +1424,7 @@ static inline bool sk_has_memory_pressure(const struct sock *sk)
 static inline bool sk_under_global_memory_pressure(const struct sock *sk)
 {
 	return sk->sk_prot->memory_pressure &&
-		!!*sk->sk_prot->memory_pressure;
+		!!READ_ONCE(*sk->sk_prot->memory_pressure);
 }
 
 static inline bool sk_under_memory_pressure(const struct sock *sk)
@@ -1435,7 +1436,7 @@ static inline bool sk_under_memory_pressure(const struct sock *sk)
 	    mem_cgroup_under_socket_pressure(sk->sk_memcg))
 		return true;
 
-	return !!*sk->sk_prot->memory_pressure;
+	return !!READ_ONCE(*sk->sk_prot->memory_pressure);
 }
 
 static inline long
@@ -1512,7 +1513,7 @@ proto_memory_pressure(struct proto *prot)
 {
 	if (!prot->memory_pressure)
 		return false;
-	return !!*prot->memory_pressure;
+	return !!READ_ONCE(*prot->memory_pressure);
 }
 
 

net/sctp/socket.c

@@ -99,7 +99,7 @@ struct percpu_counter sctp_sockets_allocated;
 
 static void sctp_enter_memory_pressure(struct sock *sk)
 {
-	sctp_memory_pressure = 1;
+	WRITE_ONCE(sctp_memory_pressure, 1);
 }