[PATCH v3] mm/memmap: Prevent double scanning of memmap by kmemleak

[PATCH v3] mm/memmap: Prevent double scanning of memmap by kmemleak

[Guo Weikang]

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>
---
v1 -> v2: Fix CI: Recover __earlyonly_bootmem_alloc that is marked with
__ref to prevent init section mismatch WARNING.
Links:  https://lore.kernel.org/oe-kbuild-all/202501021601.jub4p3EM-lkp@intel.com/
v2 -> v3: Rebase on latest mm-everything and modified some minor comments.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Links: https://lore.kernel.org/lkml/20250103110150.1352226-1-guoweikang.kernel@gmail.com/
---
 include/linux/memblock.h | 4 ++++
 mm/mm_init.c             | 8 ++++++--
 mm/sparse-vmemmap.c      | 5 +++--
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index dee628350cd1..e79eb6ac516f 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -378,6 +378,10 @@ static inline int memblock_get_region_node(const struct memblock_region *r)
 /* Flags for memblock allocation APIs */
 #define MEMBLOCK_ALLOC_ANYWHERE	(~(phys_addr_t)0)
 #define MEMBLOCK_ALLOC_ACCESSIBLE	0
+/*
+ *  MEMBLOCK_ALLOC_NOLEAKTRACE avoids kmemleak tracing. It implies
+ *  MEMBLOCK_ALLOC_ACCESSIBLE
+ */
 #define MEMBLOCK_ALLOC_NOLEAKTRACE	1
 
 /* We are using top down, so it is safe to use 0 here */
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 24b68b425afb..2630cc30147e 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1585,13 +1585,17 @@ void __init *memmap_alloc(phys_addr_t size, phys_addr_t align,
 {
 	void *ptr;
 
+	/*
+	 * Kmemleak will explicitly scan mem_map by traversing all valid
+	 * `struct *page`,so memblock does not need to be added to the scan list.
+	 */
 	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..3287ebadd167 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -31,6 +31,8 @@
 #include <asm/dma.h>
 #include <asm/pgalloc.h>
 
+#include "internal.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.
@@ -42,8 +44,7 @@ static void * __ref __earlyonly_bootmem_alloc(int node,
 				unsigned long align,
 				unsigned long goal)
 {
-	return memblock_alloc_try_nid_raw(size, align, goal,
-					       MEMBLOCK_ALLOC_ACCESSIBLE, node);
+	return memmap_alloc(size, align, goal, node, false);
 }
 
 void * __meminit vmemmap_alloc_block(unsigned long size, int node)
-- 
2.25.1

Re: [PATCH v3] mm/memmap: Prevent double scanning of memmap by kmemleak

[Catalin Marinas]

On Mon, Jan 06, 2025 at 10:11:25AM +0800, Guo Weikang wrote:
> 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>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>