From 82d8a5029a80a77166dca098b8fedb10d84e4e38 Mon Sep 17 00:00:00 2001
From: Gleb Smirnoff <glebius@FreeBSD.org>
Date: Fri, 14 Nov 2025 08:01:47 -0800
Subject: [PATCH] unix/stream: fix instant panic w/o INVARIANTS

A stupid microoptimization I made leaving empty STAILQ inconsistent
is a brainfart that is related to much earlier version of this code,
where it was safe to do so.

Pointy hat to:	glebius
Fixes:		69f61cee2efb1eec0640ca7de9b2d51599569a5d
---
 sys/kern/uipc_usrreq.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
index b1cb6de98b5..6996f3d447b 100644
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -1492,11 +1492,10 @@ uipc_soreceive_stream_or_seqpacket(struct socket *so, struct sockaddr **psa,
 	}
 
 	if (!peek) {
-		STAILQ_FIRST(&sb->uxst_mbq) = next;
-#ifdef INVARIANTS
 		if (next == NULL)
 			STAILQ_INIT(&sb->uxst_mbq);
-#endif
+		else
+			STAILQ_FIRST(&sb->uxst_mbq) = next;
 		MPASS(sb->sb_acc >= datalen);
 		sb->sb_acc -= datalen;
 		sb->sb_ccc -= datalen;