From 7162a1e87b3e380133dadc7909081bb70d0a7041 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Thu, 21 Jan 2016 16:40:27 -0800 Subject: [PATCH] mm: fix mlock accouting Tetsuo Handa reported underflow of NR_MLOCK on munlock. Testcase: #include #include #include #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 Reported-by: Tetsuo Handa Tested-by: Tetsuo Handa Cc: Michel Lespinasse Acked-by: Michal Hocko Cc: [4.4+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mlock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mlock.c b/mm/mlock.c index e1e2b1207bf2..96f001041928 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -175,7 +175,7 @@ static void __munlock_isolation_failed(struct page *page) */ 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 */ -- 2.20.1