Commit 7162a1e8 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds

mm: fix mlock accouting

Tetsuo Handa reported underflow of NR_MLOCK on munlock.


    #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,
                -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

Let's make nr_pages signed int.

Similar fixes in 6cdb18ad ("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: ff6a6da6 ("mm: accelerate munlock() treatment of THP pages")
Signed-off-by: 's avatarKirill A. Shutemov <>
Reported-by: 's avatarTetsuo Handa <>
Tested-by: 's avatarTetsuo Handa <>
Cc: Michel Lespinasse <>
Acked-by: 's avatarMichal Hocko <>
Cc: <>  [4.4+]
Signed-off-by: 's avatarAndrew Morton <>
Signed-off-by: 's avatarLinus Torvalds <>
parent b6ec57f4
......@@ -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 */
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