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

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/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>
Reported-by: "Luis R. Rodriguez" <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: "Luis R. Rodriguez" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>