Re: [akpm-mm:mm-new] BUILD REGRESSION 0bffe67ab8a72b3725cc31c4b525709bd3a3e223

[Muchun Song <muchun.song@linux.dev>]

> On Sep 10, 2026, at 06:36, Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> On Thu, 10 Sep 2026 05:56:22 +0800 kernel test robot <lkp@intel.com> wrote:
> 
>> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-new
>> branch HEAD: 0bffe67ab8a72b3725cc31c4b525709bd3a3e223  mm/swap, PM: hibernate: atomically replace hibernation pin
>> 
>> Error/Warning (recently discovered and may have been fixed):
>> 
>>    https://lore.kernel.org/oe-kbuild-all/202609100351.ALNh2KwC-lkp@intel.com
>> 
>>    include/linux/mmzone.h:1692:10: error: call to undeclared function 'NODE_DATA'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>>    include/linux/mmzone.h:1692:26: error: member reference type 'int' is not a pointer
>>    include/linux/mmzone.h:1780:35: error: conflicting types for 'NODE_DATA'
>> 
>> Error/Warning ids grouped by kconfigs:
> 
> Thanks.  That's Muchun's "mm/sparse-vmemmap: switch device DAX to
> shared tail vmemmap pages" not liking CONFIG_NUMA=n.
> 
> I'll try this nasty thing for now.  Muchun, please make it less nasty!


My bad.

device_zone() uses NODE_DATA() before it is defined when CONFIG_NUMA
is disabled. This causes non-NUMA builds with CONFIG_ZONE_DEVICE=y to
fail.

Move device_zone() after the definition of NODE_DATA() so it is available
in non-NUMA builds.

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 03ed9232f186..df42fbf3962a 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1686,21 +1686,11 @@ static inline bool zone_is_zone_device(const struct zone *zone)
 {
        return zone_idx(zone) == ZONE_DEVICE;
 }
-
-static inline struct zone *device_zone(int nid)
-{
-       return &NODE_DATA(nid)->node_zones[ZONE_DEVICE];
-}
 #else
 static inline bool zone_is_zone_device(const struct zone *zone)
 {
        return false;
 }
-
-static inline struct zone *device_zone(int nid)
-{
-       return NULL;
-}
 #endif

 /*
@@ -2159,11 +2149,21 @@ static inline int online_device_section(const struct mem_section *section)

        return section && ((section->section_mem_map & flags) == flags);
 }
+
+static inline struct zone *device_zone(int nid)
+{
+       return &NODE_DATA(nid)->node_zones[ZONE_DEVICE];
+}
 #else
 static inline int online_device_section(const struct mem_section *section)
 {
        return 0;
 }
+
+static inline struct zone *device_zone(int nid)
+{
+       return NULL;
+}
 #endif

 static inline int online_section_nr(unsigned long nr)

> 
> --- a/include/linux/mmzone.h~mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix
> +++ a/include/linux/mmzone.h
> @@ -1687,16 +1687,20 @@ static inline bool zone_is_zone_device(c
> return zone_idx(zone) == ZONE_DEVICE;
> }
> 
> +#ifdef CONFIG_NUMA
> static inline struct zone *device_zone(int nid)
> {
> 	return &NODE_DATA(nid)->node_zones[ZONE_DEVICE];
> }
> +#endif
> #else
> static inline bool zone_is_zone_device(const struct zone *zone)
> {
> 	return false;
> }
> +#endif
> 
> +#if !defined(CONFIG_ZONE_DEVICE) && !defined(CONFIG_NUMA)
> static inline struct zone *device_zone(int nid)
> {
> 	return NULL;
> _
>