linux-kernel - [PATCH v2] m68k: Define NR

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Message-ID: <20240923235617.1584056-1-linux@roeck-us.net>
Date: Mon, 23 Sep 2024 16:56:17 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: linux-m68k@...ts.linux-m68k.org
Cc: linux-kernel@...r.kernel.org,
	Guenter Roeck <linux@...ck-us.net>,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH v2] m68k: Define NR_CPUS

SPLIT_PTE_PTLOCKS depends on "NR_CPUS >= 4". Unfortunately, that evaluates
to true if there is no NR_CPUS configuration option. This results in
CONFIG_SPLIT_PTE_PTLOCKS=y for mac_defconfig. This in turn causes the m68k
"q800" and "virt" machines to crash in qemu if debugging options are
enabled.

Making CONFIG_SPLIT_PTE_PTLOCKS dependent on the existence of NR_CPUS
does not work since a dependency on the existence of a numeric Kconfig
entry always evaluates to false. Example:

config HAVE_NO_NR_CPUS
       def_bool y
       depends on !NR_CPUS

After adding this to a Kconfig file, "make defconfig" includes:
$ grep NR_CPUS .config
CONFIG_NR_CPUS=64
CONFIG_HAVE_NO_NR_CPUS=y

Define NR_CPUS for m68k instead to solve the problem.

Fixes: 394290cba966 ("mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options")
Cc: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Acked-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
v2: Instead of trying to make SPLIT_PTE_PTLOCKS depend on the 
    existence of NR_CPUS, define NR_CPUS for m68k.

v1: https://lore.kernel.org/lkml/202409240546.SJwj9tUj-lkp@intel.com/T/#t

 arch/m68k/Kconfig | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index cc26df907bfe..53e4058d2e3c 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -76,6 +76,10 @@ config PGTABLE_LEVELS
 	default 2 if SUN3 || COLDFIRE
 	default 3
 
+config NR_CPUS
+	int
+	default "1"
+
 config MMU
 	bool "MMU-based Paged Memory Management Support"
 	default y
-- 
2.45.2