From: Vitaliy Makkoveev <mvs@openbsd.org>
Subject: Make socket lock optional to sorele()
To: Alexander Bluhm <bluhm@openbsd.org>, tech@openbsd.org
Date: Thu, 2 Jan 2025 12:42:42 +0300

Previously solock() was required() to call sorele() only to make happy
the assertion within sbrelease(). Now nothing within sorele() requires
solock(), so it could be called lockless. So I propose to rename the
`kkep_lock' arg of sorele to `no_unlock' and conceptually allow this.

Now we have the only place within soclose() while solock() was taken
just to only release it. Socket splicing is about buffers, which have
their own locks, so solock() is not required in this layer, but pointers
to socket should be safe for dereference, and soref() with sorele()
are pretty enough for this.

Index: sys/kern/uipc_socket.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_socket.c,v
diff -u -p -r1.352 uipc_socket.c
--- sys/kern/uipc_socket.c	31 Dec 2024 12:19:46 -0000	1.352
+++ sys/kern/uipc_socket.c	2 Jan 2025 09:31:12 -0000
@@ -250,9 +250,9 @@ solisten(struct socket *so, int backlog)
 }
 
 void
-sorele(struct socket *so, int keep_lock)
+sorele(struct socket *so, int no_unlock)
 {
-	if (keep_lock == 0)
+	if (no_unlock == 0)
 		sounlock(so);
 
 	if (refcnt_rele(&so->so_refcnt) == 0)
@@ -438,8 +438,7 @@ discard:
 			sounlock(soback);
 		}
 		sbunlock(&soback->so_rcv);
-		solock(soback);
-		sorele(soback, 0);
+		sorele(soback, 1);
 
 notsplicedback:
 		sblock(&so->so_rcv, SBL_WAIT | SBL_NOINTR);