kmemleak: Annotate false positive in init_section_page_cgroup()

The pointer to the page_cgroup table allocated in
init_section_page_cgroup() is stored in section->page_cgroup as (base -
pfn). Since this value does not point to the beginning or inside the
allocated memory block, kmemleak reports a false positive.

This was reported in bugzilla.kernel.org as #16297.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Adrien Dessemond <adrien.dessemond@gmail.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Andrew Morton <akpm@linux-foundation.org>

mm/page_cgroup.c

@@ -9,6 +9,7 @@
 #include <linux/vmalloc.h>
 #include <linux/cgroup.h>
 #include <linux/swapops.h>
+#include <linux/kmemleak.h>
 
 static void __meminit
 __init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
@@ -126,6 +127,12 @@ static int __init_refok init_section_page_cgroup(unsigned long pfn)
 			if (!base)
 				base = vmalloc(table_size);
 		}
+		/*
+		 * The value stored in section->page_cgroup is (base - pfn)
+		 * and it does not point to the memory block allocated above,
+		 * causing kmemleak false positives.
+		 */
+		kmemleak_not_leak(base);
 	} else {
 		/*
  		 * We don't have to allocate page_cgroup again, but