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

[lirongqing]

From: Li RongQing <lirongqing@xxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxxxxx>
Cc: Harry Yoo <harry@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Hao Li <hao.li@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
---
 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