2 files changed, 20 insertions, 12 deletions

diff --git a/src/commonlib/include/commonlib/mem_pool.h b/src/commonlib/include/commonlib/mem_pool.h
index bde9e417fe..6c85397314 100644
--- a/src/commonlib/include/commonlib/mem_pool.h
+++ b/src/commonlib/include/commonlib/mem_pool.h
@@ -7,11 +7,14 @@
 #include <stdint.h>
 
 /*
- * The memory pool allows one to allocate memory from a fixed size buffer
- * that also allows freeing semantics for reuse. However, the current
- * limitation is that the most recent allocation is the only one that
- * can be freed. If one tries to free any allocation that isn't the
- * most recently allocated it will result in a leak within the memory pool.
+ * The memory pool allows one to allocate memory from a fixed size buffer that
+ * also allows freeing semantics for reuse. However, the current limitation is
+ * that only the two most recent allocations  can be freed (in exact reverse
+ * order). If one tries to free any allocation that isn't at the top of the
+ * allocation stack, or one allocates more than two buffers in a row without
+ * freeing, it will result in a leak within the memory pool. (Two allocations
+ * were chosen to optimize for the CBFS cache case which may need two buffers
+ * to map a single compressed file, and will free them in reverse order.)
  *
  * The memory returned by allocations are at least 8 byte aligned. Note
  * that this requires the backing buffer to start on at least an 8 byte
@@ -22,20 +25,23 @@ struct mem_pool {
 	uint8_t *buf;
 	size_t size;
 	uint8_t *last_alloc;
+	uint8_t *second_to_last_alloc;
 	size_t free_offset;
 };
 
-#define MEM_POOL_INIT(buf_, size_)	\
-	{				\
-		.buf = (buf_),		\
-		.size = (size_),	\
-		.last_alloc = NULL,	\
-		.free_offset = 0,	\
+#define MEM_POOL_INIT(buf_, size_)		\
+	{					\
+		.buf = (buf_),			\
+		.size = (size_),		\
+		.last_alloc = NULL,		\
+		.second_to_last_alloc = NULL,	\
+		.free_offset = 0,		\
 	}
 
 static inline void mem_pool_reset(struct mem_pool *mp)
 {
 	mp->last_alloc = NULL;
+	mp->second_to_last_alloc = NULL;
 	mp->free_offset = 0;
 }
 
diff --git a/src/commonlib/mem_pool.c b/src/commonlib/mem_pool.c
index 2ad1099d6b..c300c65d6e 100644
--- a/src/commonlib/mem_pool.c
+++ b/src/commonlib/mem_pool.c
@@ -17,6 +17,7 @@ void *mem_pool_alloc(struct mem_pool *mp, size_t sz)
 	p = &mp->buf[mp->free_offset];
 
 	mp->free_offset += sz;
+	mp->second_to_last_alloc = mp->last_alloc;
 	mp->last_alloc = p;
 
 	return p;
@@ -29,6 +30,7 @@ void mem_pool_free(struct mem_pool *mp, void *p)
 		return;
 
 	mp->free_offset = mp->last_alloc - mp->buf;
+	mp->last_alloc = mp->second_to_last_alloc;
 	/* No way to track allocation before this one. */
-	mp->last_alloc = NULL;
+	mp->second_to_last_alloc = NULL;
 }