[PATCH] mm/mempool: use static key for boot-time debug enablement

[PATCH] mm/mempool: use static key for boot-time debug enablement

[lirongqing]

From: Li RongQing <lirongqing@baidu.com>

Replace the #ifdef CONFIG_SLUB_DEBUG_ON conditional compilation with a
static key (mempool_debug_enabled). This allows enabling mempool debugging
at boot time via:

    mempool_debug

Instead of requiring CONFIG_SLUB_DEBUG_ON at compile time. Benefits:

- Debugging can be enabled without rebuilding the kernel
- Uses standard kernel static_key mechanism with minimal overhead

Suggested-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Hao Li <hao.li@linux.dev>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
---
 Documentation/admin-guide/kernel-parameters.txt |  5 ++++
 mm/mempool.c                                    | 32 ++++++++++++++++++-------
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 35ed9dc..5a070e6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3998,6 +3998,11 @@ Kernel parameters
 			Note that even when enabled, there are a few cases where
 			the feature is not effective.
 
+	mempool_debug	[MM]
+			Enable mempool debugging. This enables element
+			poison checking when freeing elements back to the
+			pool. Useful for debugging mempool corruption.
+
 	memtest=	[KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
 			Format: <integer>
 			default : 0 <disable>
diff --git a/mm/mempool.c b/mm/mempool.c
index db23e0e..4f429a1 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -16,11 +16,28 @@
 #include <linux/export.h>
 #include <linux/mempool.h>
 #include <linux/writeback.h>
+#include <linux/static_key.h>
+#include <linux/init.h>
 #include "slab.h"
 
 static DECLARE_FAULT_ATTR(fail_mempool_alloc);
 static DECLARE_FAULT_ATTR(fail_mempool_alloc_bulk);
 
+/*
+ * Debugging support for mempool using static key.
+ *
+ * This allows enabling mempool debug at boot time via:
+ *   mempool_debug
+ */
+static DEFINE_STATIC_KEY_FALSE(mempool_debug_enabled);
+
+static int __init mempool_debug_setup(char *str)
+{
+	static_branch_enable(&mempool_debug_enabled);
+	return 0;
+}
+early_param("mempool_debug", mempool_debug_setup);
+
 static int __init mempool_faul_inject_init(void)
 {
 	int error;
@@ -37,7 +54,6 @@ static int __init mempool_faul_inject_init(void)
 }
 late_initcall(mempool_faul_inject_init);
 
-#ifdef CONFIG_SLUB_DEBUG_ON
 static void poison_error(struct mempool *pool, void *element, size_t size,
 			 size_t byte)
 {
@@ -73,6 +89,9 @@ static void __check_element(struct mempool *pool, void *element, size_t size)
 
 static void check_element(struct mempool *pool, void *element)
 {
+	if (!static_branch_unlikely(&mempool_debug_enabled))
+		return;
+
 	/* Skip checking: KASAN might save its metadata in the element. */
 	if (kasan_enabled())
 		return;
@@ -112,6 +131,9 @@ static void __poison_element(void *element, size_t size)
 
 static void poison_element(struct mempool *pool, void *element)
 {
+	if (!static_branch_unlikely(&mempool_debug_enabled))
+		return;
+
 	/* Skip poisoning: KASAN might save its metadata in the element. */
 	if (kasan_enabled())
 		return;
@@ -140,14 +162,6 @@ static void poison_element(struct mempool *pool, void *element)
 #endif
 	}
 }
-#else /* CONFIG_SLUB_DEBUG_ON */
-static inline void check_element(struct mempool *pool, void *element)
-{
-}
-static inline void poison_element(struct mempool *pool, void *element)
-{
-}
-#endif /* CONFIG_SLUB_DEBUG_ON */
 
 static __always_inline bool kasan_poison_element(struct mempool *pool,
 		void *element)
-- 
2.9.4

Re: [PATCH] mm/mempool: use static key for boot-time debug enablement

[Usama Arif]

On Wed, 27 May 2026 06:46:34 -0400 lirongqing <lirongqing@baidu.com> wrote:

> From: Li RongQing <lirongqing@baidu.com>
> 
> Replace the #ifdef CONFIG_SLUB_DEBUG_ON conditional compilation with a
> static key (mempool_debug_enabled). This allows enabling mempool debugging
> at boot time via:
> 
>     mempool_debug
> 
> Instead of requiring CONFIG_SLUB_DEBUG_ON at compile time. Benefits:
> 
> - Debugging can be enabled without rebuilding the kernel
> - Uses standard kernel static_key mechanism with minimal overhead
> 
> Suggested-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> Cc: Vlastimil Babka <vbabka@kernel.org>
> Cc: Harry Yoo <harry@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Hao Li <hao.li@linux.dev>
> Cc: Christoph Lameter <cl@gentwo.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Roman Gushchin <roman.gushchin@linux.dev>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  5 ++++
>  mm/mempool.c                                    | 32 ++++++++++++++++++-------
>  2 files changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 35ed9dc..5a070e6 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3998,6 +3998,11 @@ Kernel parameters
>  			Note that even when enabled, there are a few cases where
>  			the feature is not effective.
>  
> +	mempool_debug	[MM]
> +			Enable mempool debugging. This enables element
> +			poison checking when freeing elements back to the
> +			pool. Useful for debugging mempool corruption.
> +
>  	memtest=	[KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
>  			Format: <integer>
>  			default : 0 <disable>
> diff --git a/mm/mempool.c b/mm/mempool.c
> index db23e0e..4f429a1 100644
> --- a/mm/mempool.c
> +++ b/mm/mempool.c
> @@ -16,11 +16,28 @@
>  #include <linux/export.h>
>  #include <linux/mempool.h>
>  #include <linux/writeback.h>
> +#include <linux/static_key.h>
> +#include <linux/init.h>
>  #include "slab.h"
>  
>  static DECLARE_FAULT_ATTR(fail_mempool_alloc);
>  static DECLARE_FAULT_ATTR(fail_mempool_alloc_bulk);
>  
> +/*
> + * Debugging support for mempool using static key.
> + *
> + * This allows enabling mempool debug at boot time via:
> + *   mempool_debug
> + */
> +static DEFINE_STATIC_KEY_FALSE(mempool_debug_enabled);
> +
> +static int __init mempool_debug_setup(char *str)
> +{
> +	static_branch_enable(&mempool_debug_enabled);
> +	return 0;
> +}
> +early_param("mempool_debug", mempool_debug_setup);
> +

Can static_branch_enable() in mempool_debug_setup() run before
jump_label_init() has set static_key_initialized?

Looking at start_kernel() in init/main.c:

	setup_arch(&command_line);
	mm_core_init_early();
	/* Static keys and static calls are needed by LSMs */
	jump_label_init();
	...
	/* parameters may set static keys */
	parse_early_param();

This will trigger the warning in include/linux/jump_label.h has:

	#define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \
	    "%s(): static key '%pS' used before call to jump_label_init()", \
	    __func__, (key))


mm/dmapool.c registers an equivalent debug toggle via __setup()
rather than early_param():

	static int __init dmapool_debug_setup(char *str)
	{
		static_branch_enable(&dmapool_debug_enabled);
		return 1;
	}
	__setup("dmapool_debug", dmapool_debug_setup);

I think you can reuse that.

>  static int __init mempool_faul_inject_init(void)
>  {
>  	int error;
> @@ -37,7 +54,6 @@ static int __init mempool_faul_inject_init(void)
>  }
>  late_initcall(mempool_faul_inject_init);
>  
> -#ifdef CONFIG_SLUB_DEBUG_ON
>  static void poison_error(struct mempool *pool, void *element, size_t size,
>  			 size_t byte)
>  {
> @@ -73,6 +89,9 @@ static void __check_element(struct mempool *pool, void *element, size_t size)
>  
>  static void check_element(struct mempool *pool, void *element)
>  {
> +	if (!static_branch_unlikely(&mempool_debug_enabled))
> +		return;
> +
>  	/* Skip checking: KASAN might save its metadata in the element. */
>  	if (kasan_enabled())
>  		return;
> @@ -112,6 +131,9 @@ static void __poison_element(void *element, size_t size)
>  
>  static void poison_element(struct mempool *pool, void *element)
>  {
> +	if (!static_branch_unlikely(&mempool_debug_enabled))
> +		return;
> +

Before this change, building with CONFIG_SLUB_DEBUG_ON=y compiled in
check_element() and poison_element() unconditionally, so the
poisoning and corruption checks ran on every mempool free/alloc.
After this change those checks are gated on the mempool_debug boot
parameter even when CONFIG_SLUB_DEBUG_ON=y.

Existing users who relied on CONFIG_SLUB_DEBUG_ON=y giving them
mempool poison checking will silently lose it on upgrade unless they
also add "mempool_debug" to the command line.

Would it be worth defaulting the static key to true under
CONFIG_SLUB_DEBUG_ON=y, for example:

	#ifdef CONFIG_SLUB_DEBUG_ON
	static DEFINE_STATIC_KEY_TRUE(mempool_debug_enabled);
	#else
	static DEFINE_STATIC_KEY_FALSE(mempool_debug_enabled);
	#endif

so the previous default behaviour is preserved.


>  	/* Skip poisoning: KASAN might save its metadata in the element. */
>  	if (kasan_enabled())
>  		return;
> @@ -140,14 +162,6 @@ static void poison_element(struct mempool *pool, void *element)
>  #endif
>  	}
>  }
> -#else /* CONFIG_SLUB_DEBUG_ON */
> -static inline void check_element(struct mempool *pool, void *element)
> -{
> -}
> -static inline void poison_element(struct mempool *pool, void *element)
> -{
> -}
> -#endif /* CONFIG_SLUB_DEBUG_ON */
>  
>  static __always_inline bool kasan_poison_element(struct mempool *pool,
>  		void *element)
> -- 
> 2.9.4
> 
> 

Re: [PATCH] mm/mempool: use static key for boot-time debug enablement

[Vlastimil Babka (SUSE)]

On 5/27/26 15:03, Usama Arif wrote:
> On Wed, 27 May 2026 06:46:34 -0400 lirongqing <lirongqing@baidu.com> wrote:
>>  static int __init mempool_faul_inject_init(void)
>>  {
>>  	int error;
>> @@ -37,7 +54,6 @@ static int __init mempool_faul_inject_init(void)
>>  }
>>  late_initcall(mempool_faul_inject_init);
>>  
>> -#ifdef CONFIG_SLUB_DEBUG_ON
>>  static void poison_error(struct mempool *pool, void *element, size_t size,
>>  			 size_t byte)
>>  {
>> @@ -73,6 +89,9 @@ static void __check_element(struct mempool *pool, void *element, size_t size)
>>  
>>  static void check_element(struct mempool *pool, void *element)
>>  {
>> +	if (!static_branch_unlikely(&mempool_debug_enabled))
>> +		return;
>> +
>>  	/* Skip checking: KASAN might save its metadata in the element. */
>>  	if (kasan_enabled())
>>  		return;
>> @@ -112,6 +131,9 @@ static void __poison_element(void *element, size_t size)
>>  
>>  static void poison_element(struct mempool *pool, void *element)
>>  {
>> +	if (!static_branch_unlikely(&mempool_debug_enabled))
>> +		return;
>> +
> 
> Before this change, building with CONFIG_SLUB_DEBUG_ON=y compiled in
> check_element() and poison_element() unconditionally, so the
> poisoning and corruption checks ran on every mempool free/alloc.
> After this change those checks are gated on the mempool_debug boot
> parameter even when CONFIG_SLUB_DEBUG_ON=y.

The same would apply to the dmapool_debug [1]

https://lore.kernel.org/all/20260524034015.1830-1-lirongqing@baidu.com/

> Existing users who relied on CONFIG_SLUB_DEBUG_ON=y giving them
> mempool poison checking will silently lose it on upgrade unless they
> also add "mempool_debug" to the command line.
> 
> Would it be worth defaulting the static key to true under
> CONFIG_SLUB_DEBUG_ON=y, for example:
> 
> 	#ifdef CONFIG_SLUB_DEBUG_ON
> 	static DEFINE_STATIC_KEY_TRUE(mempool_debug_enabled);
> 	#else
> 	static DEFINE_STATIC_KEY_FALSE(mempool_debug_enabled);
> 	#endif
> 
> so the previous default behaviour is preserved.

There's DEFINE_STATIC_KEY_MAYBE for this.

But I think nobody will care really. My objection was that this and
dmapool_debug was tied to CONFIG_SLUB_DEBUG_ON in the first place, despite
not being part of slab. I'd rather disconnect it completely.

If testing bots relied on this, we could give them heads up to start using
those boot options. I assume they already use some for stuff that has no
CONFIG_ enablement.

>>  	/* Skip poisoning: KASAN might save its metadata in the element. */
>>  	if (kasan_enabled())
>>  		return;
>> @@ -140,14 +162,6 @@ static void poison_element(struct mempool *pool, void *element)
>>  #endif
>>  	}
>>  }
>> -#else /* CONFIG_SLUB_DEBUG_ON */
>> -static inline void check_element(struct mempool *pool, void *element)
>> -{
>> -}
>> -static inline void poison_element(struct mempool *pool, void *element)
>> -{
>> -}
>> -#endif /* CONFIG_SLUB_DEBUG_ON */
>>  
>>  static __always_inline bool kasan_poison_element(struct mempool *pool,
>>  		void *element)
>> -- 
>> 2.9.4
>> 
>>