On Tue 19-01-16 14:21:01, Kirill A. Shutemov wrote:
[...]
> >From 6f80a79dc5f65f29899e396942d40f727cd36480 Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Tue, 19 Jan 2016 14:59:19 +0300
> Subject: [PATCH] mm: fix mlock accouting
>
> 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 singed int.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Fixes: ff6a6da60b89 ("mm: accelerate munlock() treatment of THP pages")
> Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Michel Lespinasse <walken@xxxxxxxxxx>
$ grep Mlocked /proc/meminfo
Mlocked: 10840497455108 kB
I've started seeing the same issue recently but was too busy to track it
down. Thanks! Mentioning 6cdb18ad98a4 ("mm/vmstat: fix overflow in
mod_zone_page_state()") would be really helpful here.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> 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 */
> --
> Kirill A. Shutemov
>
> --
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--
Michal Hocko
SUSE Labs
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