From: Vitaliy Makkoveev <mvs@openbsd.org>
Subject: Use WRITE_ONCE() to se set so_error in sosend()/soreceive()
To: Alexander Bluhm <bluhm@openbsd.org>, tech@openbsd.org
Date: Mon, 6 Jan 2025 18:58:16 +0300

This is the lockless access, so do it. 

Index: sys/kern/uipc_socket.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_socket.c,v
diff -u -p -r1.356 uipc_socket.c
--- sys/kern/uipc_socket.c	4 Jan 2025 15:57:02 -0000	1.356
+++ sys/kern/uipc_socket.c	6 Jan 2025 15:53:54 -0000
@@ -640,7 +640,7 @@ restart:
 		if (so->so_snd.sb_state & SS_CANTSENDMORE)
 			snderr(EPIPE);
 		if ((error = READ_ONCE(so->so_error))) {
-			so->so_error = 0;
+			WRITE_ONCE(so->so_error, 0);
 			snderr(error);
 		}
 		if ((so->so_state & SS_ISCONNECTED) == 0) {
@@ -934,7 +934,7 @@ restart:
 				goto dontblock;
 			error = error2;
 			if ((flags & MSG_PEEK) == 0)
-				so->so_error = 0;
+				WRITE_ONCE(so->so_error, 0);
 			goto release;
 		}
 		if (so->so_rcv.sb_state & SS_CANTRCVMORE) {
@@ -1204,7 +1204,7 @@ dontblock:
 		while (flags & MSG_WAITALL && m == NULL && uio->uio_resid > 0 &&
 		    !sosendallatonce(so) && !nextrecord) {
 			if (so->so_rcv.sb_state & SS_CANTRCVMORE ||
-			    so->so_error)
+			    READ_ONCE(so->so_error))
 				break;
 			SBLASTRECORDCHK(&so->so_rcv, "soreceive sbwait 2");
 			SBLASTMBUFCHK(&so->so_rcv, "soreceive sbwait 2");