The patch titled
Subject: mm: make SPLIT_PTE_PTLOCKS depend on SMP
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-make-split_pte_ptlocks-depend-on-smp.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-make-split_pte_ptlocks-depend-on-smp.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Guenter Roeck <linux@xxxxxxxxxxxx>
Subject: mm: make SPLIT_PTE_PTLOCKS depend on SMP
Date: Tue, 24 Sep 2024 08:42:05 -0700
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
Defining NR_CPUS for m68k does not help either since many architectures
define NR_CPUS only for SMP configurations.
Make SPLIT_PTE_PTLOCKS depend on SMP instead to solve the problem.
Link: https://lkml.kernel.org/r/20240924154205.1491376-1-linux@xxxxxxxxxxxx
Fixes: 394290cba966 ("mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options")
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/Kconfig | 1 +
1 file changed, 1 insertion(+)
--- a/mm/Kconfig~mm-make-split_pte_ptlocks-depend-on-smp
+++ a/mm/Kconfig
@@ -595,6 +595,7 @@ config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
config SPLIT_PTE_PTLOCKS
def_bool y
depends on MMU
+ depends on SMP
depends on NR_CPUS >= 4
depends on !ARM || CPU_CACHE_VIPT
depends on !PARISC || PA20
_
Patches currently in -mm which might be from linux@xxxxxxxxxxxx are
mm-make-split_pte_ptlocks-depend-on-smp.patch
