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

Commit 248ac0e1943a ("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).

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>

1 files changed, 10 insertions, 4 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 745fa9567475..0fdf96803c5b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -359,6 +359,12 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
         if (unlikely(!va))
                 return ERR_PTR(-ENOMEM);
 
+        /*
+         * Only scan the relevant parts containing pointers to other objects
+         * to avoid false negatives.
+         */
+        kmemleak_scan_area(&va->rb_node, SIZE_MAX, gfp_mask & GFP_RECLAIM_MASK);
+
 retry:
         spin_lock(&vmap_area_lock);
         /*
@@ -1645,11 +1651,11 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
         clear_vm_uninitialized_flag(area);
 
         /*
-         * A ref_count = 3 is needed because the vm_struct and vmap_area
-         * structures allocated in the __get_vm_area_node() function contain
-         * references to the virtual address of the vmalloc'ed block.
+         * 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, 3, gfp_mask);
+        kmemleak_alloc(addr, real_size, 2, gfp_mask);
 
         return addr;