[PATCH] mm: add missing alloc_percpu() NULL check in hotplug init

[PATCH] mm: add missing alloc_percpu() NULL check in hotplug init

[Hongfu Li]

From: Hongfu Li <lihongfu@kylinos.cn>

No NULL check is done for alloc_percpu() when initializing per-CPU
nodestats. Allocation failure leads to NULL pointer dereference
during later memset.

Make function return int, check alloc_percpu() result and return
-ENOMEM on error. The caller chain already propagates this error
correctly.

Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
---
 include/linux/memory_hotplug.h |  2 +-
 mm/memory_hotplug.c            |  3 ++-
 mm/mm_init.c                   | 14 +++++++++++---
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 7c9d66729c60..f04b915678db 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -289,7 +289,7 @@ static inline void __remove_memory(u64 start, u64 size) {}
 /* Default online_type (MMOP_*) when new memory blocks are added. */
 extern enum mmop mhp_get_default_online_type(void);
 extern void mhp_set_default_online_type(enum mmop online_type);
-extern void __ref free_area_init_core_hotplug(struct pglist_data *pgdat);
+extern int __ref free_area_init_core_hotplug(struct pglist_data *pgdat);
 extern int __add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags);
 extern int add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags);
 extern int add_memory_resource(int nid, struct resource *resource,
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 7ac19fab2263..8b137328dcf0 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1263,7 +1263,8 @@ static pg_data_t *hotadd_init_pgdat(int nid)
 	pgdat = NODE_DATA(nid);
 
 	/* init node's zones as empty zones, we don't have any present pages.*/
-	free_area_init_core_hotplug(pgdat);
+	if (free_area_init_core_hotplug(pgdat))
+		return NULL;
 
 	/*
 	 * The node we allocated has no zone fallback lists. For avoiding
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 0f64909e8d20..24770947a66f 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1536,7 +1536,7 @@ void __init set_pageblock_order(void)
  * NOTE: this function is only called during memory hotplug
  */
 #ifdef CONFIG_MEMORY_HOTPLUG
-void __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
+int __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
 {
 	int nid = pgdat->node_id;
 	enum zone_type z;
@@ -1544,8 +1544,14 @@ void __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
 
 	pgdat_init_internals(pgdat);
 
-	if (pgdat->per_cpu_nodestats == &boot_nodestats)
-		pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat);
+	if (pgdat->per_cpu_nodestats == &boot_nodestats) {
+		struct per_cpu_nodestat __percpu *new;
+
+		new = alloc_percpu(struct per_cpu_nodestat);
+		if (!new)
+			return -ENOMEM;
+		pgdat->per_cpu_nodestats = new;
+	}
 
 	/*
 	 * Reset the nr_zones, order and highest_zoneidx before reuse.
@@ -1576,6 +1582,8 @@ void __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
 		zone->present_pages = 0;
 		zone_init_internals(zone, z, nid, 0);
 	}
+
+	return 0;
 }
 #endif
 
-- 
2.54.0

Re: [PATCH] mm: add missing alloc_percpu() NULL check in hotplug init

[Mike Rapoport]

On Fri, Jul 17, 2026 at 01:29:38PM +0800, Hongfu Li wrote:
> From: Hongfu Li <lihongfu@kylinos.cn>
> 
> No NULL check is done for alloc_percpu() when initializing per-CPU
> nodestats. Allocation failure leads to NULL pointer dereference
> during later memset.
> 
> Make function return int, check alloc_percpu() result and return
> -ENOMEM on error. The caller chain already propagates this error
> correctly.

I already applied a fix from Gregory:

https://patch.msgid.link/20260701221613.2818148-1-gourry@gourry.net

It'll be unstreamed soon.
 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
> ---
>  include/linux/memory_hotplug.h |  2 +-
>  mm/memory_hotplug.c            |  3 ++-
>  mm/mm_init.c                   | 14 +++++++++++---
>  3 files changed, 14 insertions(+), 5 deletions(-)

-- 
Sincerely yours,
Mike.

Re: [PATCH] mm: add missing alloc_percpu() NULL check in hotplug init

[Hongfu Li]

On 7/17/26 2:46 PM, Mike Rapoport wrote:
> On Fri, Jul 17, 2026 at 01:29:38PM +0800, Hongfu Li wrote:
>> From: Hongfu Li <lihongfu@kylinos.cn>
>>
>> No NULL check is done for alloc_percpu() when initializing per-CPU
>> nodestats. Allocation failure leads to NULL pointer dereference
>> during later memset.
>>
>> Make function return int, check alloc_percpu() result and return
>> -ENOMEM on error. The caller chain already propagates this error
>> correctly.
> I already applied a fix from Gregory:
>
> https://patch.msgid.link/20260701221613.2818148-1-gourry@gourry.net
>
> It'll be unstreamed soon.

Got it, I'll drop this patch as Gregory's fix is already on the way 
upstream.