mm: kmemleak: avoid false negatives on vmalloc'ed objects

Commit 248ac0e1 ("mm/vmalloc: remove guard page from between vmap
blocks") had the side effect of making vmap_area.va_end member point to
the next vmap_area.va_start.  This was creating an artificial reference
to vmalloc'ed objects and kmemleak was rarely reporting vmalloc() leaks.

This patch marks the vmap_area containing pointers explicitly and
reduces the min ref_count to 2 as vm_struct still contains a reference
to the vmalloc'ed object.  The kmemleak add_scan_area() function has
been improved to allow a SIZE_MAX argument covering the rest of the
object (for simpler calling sites).

Change-Id: I237dd983d000c956ede36b5492dfe046a3060ce4
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 7f88f88f83ed609650a01b18572e605ea50cd163
Git-repo: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/


Signed-off-by: Vignesh Radhakrishnan <vigneshr@codeaurora.org>