[PATCH 4.4 093/137] mm: fix mlock accouting

Greg Kroah-Hartman
2016-02-24T04:14:39Z

From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

commit 7162a1e87b3e380133dadc7909081bb70d0a7041 upstream.

Tetsuo Handa reported underflow of NR_MLOCK on munlock.

Testcase:

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>

#define BASE ((void *)0x400000000000)
#define SIZE (1UL << 21)

int main(int argc, char *argv[])
{
void *addr;

system("grep Mlocked /proc/meminfo");
addr = mmap(BASE, SIZE, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE | MAP_LOCKED | MAP_FIXED,
-1, 0);
if (addr == MAP_FAILED)
printf("mmap() failed\n"), exit(1);
munmap(addr, SIZE);
system("grep Mlocked /proc/meminfo");
return 0;
}

It happens on munlock_vma_page() due to unfortunate choice of nr_pages
data type:

__mod_zone_page_state(zone, NR_MLOCK, -nr_pages);

For unsigned int nr_pages, implicitly casted to long in
__mod_zone_page_state(), it becomes something around UINT_MAX.

munlock_vma_page() usually called for THP as small pages go though
pagevec.

Let's make nr_pages signed int.

Similar fixes in 6cdb18ad98a4 ("mm/vmstat: fix overflow in
mod_zone_page_state()") used `long' type, but `int' here is OK for a
count of the number of sub-pages in a huge page.

Fixes: ff6a6da60b89 ("mm: accelerate munlock() treatment of THP pages")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Michel Lespinasse <walken@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/mlock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -172,7 +172,7 @@ static void __munlock_isolation_failed(s
*/
unsigned int munlock_vma_page(struct page *page)
{
- unsigned int nr_pages;
+ int nr_pages;
struct zone *zone = page_zone(page);

/* For try_to_munlock() and to serialize with page migration */