mm: kmemleak: treat vm_struct as alternative reference to vmalloc'ed objects

Kmemleak requires that vmalloc'ed objects have a minimum reference count
of 2: one in the corresponding vm_struct object and the other owned by
the vmalloc() caller.  There are cases, however, where the original
vmalloc() returned pointer is lost and, instead, a pointer to vm_struct
is stored (see free_thread_stack()).  Kmemleak currently reports such
objects as leaks.

This patch adds support for treating any surplus references to an object
as additional references to a specified object.  It introduces the
kmemleak_vmalloc() API function which takes a vm_struct pointer and sets
its surplus reference passing to the actual vmalloc() returned pointer.
The __vmalloc_node_range() calling site has been modified accordingly.

Link: http://lkml.kernel.org/r/1495726937-23557-4-git-send-email-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 6 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ecc97f74ab18..6211a807cb31 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1770,12 +1770,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	 */
 	clear_vm_uninitialized_flag(area);
 
-	/*
-	 * A ref_count = 2 is needed because vm_struct allocated in
-	 * __get_vm_area_node() contains a reference to the virtual address of
-	 * the vmalloc'ed block.
-	 */
-	kmemleak_alloc(addr, real_size, 2, gfp_mask);
+	kmemleak_vmalloc(area, size, gfp_mask);
 
 	return addr;