From d0f67f97579f7b2febf29264b1874a95056dec06 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sun, 7 May 2023 21:37:42 +0300
Subject: [PATCH] smp_topo(): make it idempotent

If more than one call to the function occurs, it currently allocates the
same amount from the group[] array, eventually leading to the memory
corruption.

Noted and reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D39981
---
 sys/kern/subr_smp.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/sys/kern/subr_smp.c b/sys/kern/subr_smp.c
index df82d948afb0..5a9aeb5ab04a 100644
--- a/sys/kern/subr_smp.c
+++ b/sys/kern/subr_smp.c
@@ -645,7 +645,14 @@ struct cpu_group *
 smp_topo(void)
 {
 	char cpusetbuf[CPUSETBUFSIZ], cpusetbuf2[CPUSETBUFSIZ];
-	struct cpu_group *top;
+	static struct cpu_group *top = NULL;
+
+	/*
+	 * The first call to smp_topo() is guaranteed to occur
+	 * during the kernel boot while we are still single-threaded.
+	 */
+	if (top != NULL)
+		return (top);
 
 	/*
 	 * Check for a fake topology request for debugging purposes.