Re: [PATCH] userfaultfd/shmem: fix minor fault page leak

[Andrew Morton]

On Mon, 22 Mar 2021 13:48:35 -0700 Axel Rasmussen <axelrasmussen@xxxxxxxxxx> wrote:

> This fix is analogous to Peter Xu's fix for hugetlb [0]. If we don't
> put_page() after getting the page out of the page cache, we leak the
> reference.
> 
> The fix can be verified by checking /proc/meminfo and running the
> userfaultfd selftest in shmem mode. Without the fix, we see MemFree /
> MemAvailable steadily decreasing with each run of the test. With the
> fix, memory is correctly freed after the test program exits.
> 
> Fixes: 00da60b9d0a0 ("userfaultfd: support minor fault handling for shmem")

Confused.  The affected code:

> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1831,6 +1831,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>  
>  	if (page && vma && userfaultfd_minor(vma)) {
>  		unlock_page(page);
> +		put_page(page);
>  		*fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
>  		return 0;
>  	}

Is added by Peter's "page && vma && userfaultfd_minor".  I assume that
"Fixes:" is incorrect?