[PATCH] mm/memmap: Prevent double scanning of memmap by kmemleak

[Guo Weikang <guoweikang.kernel@gmail.com>]

kmemleak explicitly scans the mem_map through the valid struct page objects.
However, memmap_alloc() was also adding this memory to the gray object list,
causing it to be scanned twice. Removes memmap_alloc() from the
scan list and adds a comment to clarify the behavior.

Link: https://lore.kernel.org/lkml/CAOm6qn=FVeTpH54wGDFMHuCOeYtvoTx30ktnv9-w3Nh8RMofEA@mail.gmail.com/

Signed-off-by: Guo Weikang <guoweikang.kernel@gmail.com>
---
 include/linux/memblock.h |  8 +++++++-
 mm/mm_init.c             |  8 ++++++--
 mm/sparse-vmemmap.c      | 20 ++------------------
 3 files changed, 15 insertions(+), 21 deletions(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 673d5cae7c81..b0483c534ef7 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -375,7 +375,13 @@ static inline int memblock_get_region_node(const struct memblock_region *r)
 }
 #endif /* CONFIG_NUMA */
 
-/* Flags for memblock allocation APIs */
+/*
+ * Flags for memblock allocation APIs
+ * MEMBLOCK_ALLOC_ANYWHERE and MEMBLOCK_ALLOC_ACCESSIBLE
+ * indicates wheather the allocation is limited by memblock.current_limit.
+ * MEMBLOCK_ALLOC_NOLEAKTRACE not only indicates that it does not need to
+ * be scanned by kmemleak, but also implies MEMBLOCK_ALLOC_ACCESSIBLE
+ */
 #define MEMBLOCK_ALLOC_ANYWHERE	(~(phys_addr_t)0)
 #define MEMBLOCK_ALLOC_ACCESSIBLE	0
 #define MEMBLOCK_ALLOC_NOLEAKTRACE	1
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 24b68b425afb..71b58f5f2492 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1580,6 +1580,10 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 	}
 }
 
+/*
+ * Kmemleak will explicitly scan mem_map by traversing all valid `struct *page`,
+ * so memblock does not need to be added to the scan list.
+ */
 void __init *memmap_alloc(phys_addr_t size, phys_addr_t align,
 			  phys_addr_t min_addr, int nid, bool exact_nid)
 {
@@ -1587,11 +1591,11 @@ void __init *memmap_alloc(phys_addr_t size, phys_addr_t align,
 
 	if (exact_nid)
 		ptr = memblock_alloc_exact_nid_raw(size, align, min_addr,
-						   MEMBLOCK_ALLOC_ACCESSIBLE,
+						   MEMBLOCK_ALLOC_NOLEAKTRACE,
 						   nid);
 	else
 		ptr = memblock_alloc_try_nid_raw(size, align, min_addr,
-						 MEMBLOCK_ALLOC_ACCESSIBLE,
+						 MEMBLOCK_ALLOC_NOLEAKTRACE,
 						 nid);
 
 	if (ptr && size > 0)
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index cec67c5f37d8..b6ac9b1d4ff7 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -27,25 +27,10 @@
 #include <linux/spinlock.h>
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
-
+#include "internal.h"
 #include <asm/dma.h>
 #include <asm/pgalloc.h>
 
-/*
- * Allocate a block of memory to be used to back the virtual memory map
- * or to back the page tables that are used to create the mapping.
- * Uses the main allocators if they are available, else bootmem.
- */
-
-static void * __ref __earlyonly_bootmem_alloc(int node,
-				unsigned long size,
-				unsigned long align,
-				unsigned long goal)
-{
-	return memblock_alloc_try_nid_raw(size, align, goal,
-					       MEMBLOCK_ALLOC_ACCESSIBLE, node);
-}
-
 void * __meminit vmemmap_alloc_block(unsigned long size, int node)
 {
 	/* If the main allocator is up use that, fallback to bootmem. */
@@ -66,8 +51,7 @@ void * __meminit vmemmap_alloc_block(unsigned long size, int node)
 		}
 		return NULL;
 	} else
-		return __earlyonly_bootmem_alloc(node, size, size,
-				__pa(MAX_DMA_ADDRESS));
+		return memmap_alloc(size, size, __pa(MAX_DMA_ADDRESS), node, false);
 }
 
 static void * __meminit altmap_alloc_block_buf(unsigned long size,
-- 
2.25.1