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.
Fixes: 394290cba966 ("mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options")
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
v3: Make SPLIT_PTE_PTLOCKS depend on SMP instead of defining NR_CPUS
for m68k.
Drop David's Acked-by: tag.
v2: Instead of trying to make SPLIT_PTE_PTLOCKS depend on the
existence of NR_CPUS, define NR_CPUS for m68k.
https://lore.kernel.org/lkml/20240923235617.1584056-1-linux@xxxxxxxxxxxx/
v1: https://lore.kernel.org/lkml/20240923142533.1197982-1-linux@xxxxxxxxxxxx/
mm/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/mm/Kconfig b/mm/Kconfig
index e85164c2812b..33fa51d608dc 100644
--- a/mm/Kconfig
+++ b/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
--
2.45.2
