From: Li RongQing <lirongqing@baidu.com>

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

    dmapool_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: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  5 +++
 mm/dmapool.c                                    | 52 ++++++++++++++-----------
 2 files changed, 34 insertions(+), 23 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 4d0f545..35ed9dc 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1333,6 +1333,11 @@ Kernel parameters
 
 	dis_ucode_ldr	[X86] Disable the microcode loader.
 
+	dmapool_debug	[MM]
+			Enable DMA pool debugging. This enables memory
+			poisoning and validation for DMA pool allocations.
+			Useful for debugging DMA API misuse.
+
 	dma_debug=off	If the kernel is compiled with DMA_API_DEBUG support,
 			this option disables the debugging code at boot.
 
diff --git a/mm/dmapool.c b/mm/dmapool.c
index 5d8af6e..d26f19c 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -35,10 +35,23 @@
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/wait.h>
+#include <linux/static_key.h>
+#include <linux/init.h>
 
-#ifdef CONFIG_SLUB_DEBUG_ON
-#define DMAPOOL_DEBUG 1
-#endif
+/*
+ * Debugging support for dmapool using static key.
+ *
+ * This allows enabling dmapool debug at boot time via:
+ *   dmapool_debug
+ */
+static DEFINE_STATIC_KEY_FALSE(dmapool_debug_enabled);
+
+static int __init dmapool_debug_setup(char *str)
+{
+	static_branch_enable(&dmapool_debug_enabled);
+	return 1;
+}
+__setup("dmapool_debug", dmapool_debug_setup);
 
 struct dma_block {
 	struct dma_block *next_block;
@@ -92,13 +105,15 @@ static ssize_t pools_show(struct device *dev, struct device_attribute *attr, cha
 
 static DEVICE_ATTR_RO(pools);
 
-#ifdef DMAPOOL_DEBUG
 static void pool_check_block(struct dma_pool *pool, struct dma_block *block,
 			     gfp_t mem_flags)
 {
 	u8 *data = (void *)block;
 	int i;
 
+	if (!static_branch_unlikely(&dmapool_debug_enabled))
+		return;
+
 	for (i = sizeof(struct dma_block); i < pool->size; i++) {
 		if (data[i] == POOL_POISON_FREED)
 			continue;
@@ -133,8 +148,14 @@ static struct dma_page *pool_find_page(struct dma_pool *pool, dma_addr_t dma)
 
 static bool pool_block_err(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 {
-	struct dma_block *block = pool->next_block;
 	struct dma_page *page;
+	struct dma_block *block;
+
+	if (!static_branch_unlikely(&dmapool_debug_enabled)) {
+		if (want_init_on_free())
+			memset(vaddr, 0, pool->size);
+		return false;
+	}
 
 	page = pool_find_page(pool, dma);
 	if (!page) {
@@ -143,6 +164,7 @@ static bool pool_block_err(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 		return true;
 	}
 
+	block = pool->next_block;
 	while (block) {
 		if (block != vaddr) {
 			block = block->next_block;
@@ -159,25 +181,9 @@ static bool pool_block_err(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 
 static void pool_init_page(struct dma_pool *pool, struct dma_page *page)
 {
-	memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
-}
-#else
-static void pool_check_block(struct dma_pool *pool, struct dma_block *block,
-			     gfp_t mem_flags)
-{
-}
-
-static bool pool_block_err(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
-{
-	if (want_init_on_free())
-		memset(vaddr, 0, pool->size);
-	return false;
-}
-
-static void pool_init_page(struct dma_pool *pool, struct dma_page *page)
-{
+	if (static_branch_unlikely(&dmapool_debug_enabled))
+		memset(page->vaddr, POOL_POISON_FREED, pool->allocation);
 }
-#endif
 
 static struct dma_block *pool_block_pop(struct dma_pool *pool)
 {
-- 
2.9.4