[patch 2/2] mm, mempool: poison elements backed by page allocator

[David Rientjes <rientjes@google.com>]

Elements backed by the slab allocator are poisoned when added to a
mempool's reserved pool.

It is also possible to poison elements backed by the page allocator
because the mempool layer knows the allocation order.

This patch extends mempool element poisoning to include memory backed by
the page allocator.

This is only effective for configs with CONFIG_DEBUG_VM.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/mempool.c | 74 ++++++++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 49 insertions(+), 25 deletions(-)

diff --git a/mm/mempool.c b/mm/mempool.c
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -6,6 +6,7 @@
  *  extreme VM load.
  *
  *  started by Ingo Molnar, Copyright (C) 2001
+ *  debugging by David Rientjes, Copyright (C) 2015
  */
 
 #include <linux/mm.h>
@@ -34,41 +35,64 @@ static void poison_error(mempool_t *pool, void *element, size_t size,
 	dump_stack();
 }
 
-static void check_slab_element(mempool_t *pool, void *element)
+static void __check_element(mempool_t *pool, void *element, size_t size)
 {
-	if (pool->free == mempool_free_slab || pool->free == mempool_kfree) {
-		size_t size = ksize(element);
-		u8 *obj = element;
-		size_t i;
-
-		for (i = 0; i < size; i++) {
-			u8 exp = (i < size - 1) ? POISON_FREE : POISON_END;
-
-			if (obj[i] != exp) {
-				poison_error(pool, element, size, i);
-				return;
-			}
+	u8 *obj = element;
+	size_t i;
+
+	for (i = 0; i < size; i++) {
+		u8 exp = (i < size - 1) ? POISON_FREE : POISON_END;
+
+		if (obj[i] != exp) {
+			poison_error(pool, element, size, i);
+			return;
 		}
-		memset(obj, POISON_INUSE, size);
+	}
+	memset(obj, POISON_INUSE, size);
+}
+
+static void check_element(mempool_t *pool, void *element)
+{
+	/* Mempools backed by slab allocator */
+	if (pool->free == mempool_free_slab || pool->free == mempool_kfree)
+		__check_element(pool, element, ksize(element));
+
+	/* Mempools backed by page allocator */
+	if (pool->free == mempool_free_pages) {
+		int order = (int)(long)pool->pool_data;
+		void *addr = page_address(element);
+
+		__check_element(pool, addr, 1UL << (PAGE_SHIFT + order));
 	}
 }
 
-static void poison_slab_element(mempool_t *pool, void *element)
+static void __poison_element(void *element, size_t size)
 {
-	if (pool->alloc == mempool_alloc_slab ||
-	    pool->alloc == mempool_kmalloc) {
-		size_t size = ksize(element);
-		u8 *obj = element;
+	u8 *obj = element;
+
+	memset(obj, POISON_FREE, size - 1);
+	obj[size - 1] = POISON_END;
+}
+
+static void poison_element(mempool_t *pool, void *element)
+{
+	/* Mempools backed by slab allocator */
+	if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc)
+		__poison_element(element, ksize(element));
+
+	/* Mempools backed by page allocator */
+	if (pool->alloc == mempool_alloc_pages) {
+		int order = (int)(long)pool->pool_data;
+		void *addr = page_address(element);
 
-		memset(obj, POISON_FREE, size - 1);
-		obj[size - 1] = POISON_END;
+		__poison_element(addr, 1UL << (PAGE_SHIFT + order));
 	}
 }
 #else /* CONFIG_DEBUG_VM */
-static inline void check_slab_element(mempool_t *pool, void *element)
+static inline void check_element(mempool_t *pool, void *element)
 {
 }
-static inline void poison_slab_element(mempool_t *pool, void *element)
+static inline void poison_element(mempool_t *pool, void *element)
 {
 }
 #endif /* CONFIG_DEBUG_VM */
@@ -76,7 +100,7 @@ static inline void poison_slab_element(mempool_t *pool, void *element)
 static void add_element(mempool_t *pool, void *element)
 {
 	BUG_ON(pool->curr_nr >= pool->min_nr);
-	poison_slab_element(pool, element);
+	poison_element(pool, element);
 	pool->elements[pool->curr_nr++] = element;
 }
 
@@ -85,7 +109,7 @@ static void *remove_element(mempool_t *pool)
 	void *element = pool->elements[--pool->curr_nr];
 
 	BUG_ON(pool->curr_nr < 0);
-	check_slab_element(pool, element);
+	check_element(pool, element);
 	return element;
 }