Re: [PATCH 3.14 52/70] mm: fix mlock accouting

[Luis Henriques]

On Tue, Feb 23, 2016 at 07:34:01PM -0800, Greg Kroah-Hartman wrote:
> 3.14-stable review patch.  If anyone has any objections, please let me know.
>

I'm not sure this should be queued for the 3.14 kernel.  It is tagged
for 4.4+ and since in this kernel version __mod_zone_page_state()
doesn't actually cast nr_pages to long, this patch doesn't seem to be
required.

Cheers,
--
Luís

> ------------------
> 
> From: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxx>
> Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Tested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Michel Lespinasse <walken@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> ---
>  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 */
> 
> 
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