linux-kernel - Re: [PATCH] userfaultfd/hugetlbfs: Fix minor fault page leak

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Date:   Mon, 22 Mar 2021 13:13:15 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: Re: [PATCH] userfaultfd/hugetlbfs: Fix minor fault page leak

On 3/22/21 10:51 AM, Peter Xu wrote:
> When uffd-minor enabled, we need to put the page cache before handling the
> userfault in hugetlb_no_page(), otherwise the page refcount got leaked.
> 
> This can be reproduced by running userfaultfd selftest with hugetlb_shared
> mode, then cat /proc/meminfo.
> 
> Cc: Axel Rasmussen <axelrasmussen@...gle.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Fixes: f2bf15fb0969 ("userfaultfd: add minor fault registration mode")
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  mm/hugetlb.c | 1 +
>  1 file changed, 1 insertion(+)

Thanks for finding/fixing.

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

I think this is just in Andrew's tree.  So it will need to be fixed
there.
-- 
Mike Kravetz

> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 408dbc08298a..56b78a206913 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4449,6 +4449,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
>  		/* Check for page in userfault range. */
>  		if (userfaultfd_minor(vma)) {
>  			unlock_page(page);
> +			put_page(page);
>  			ret = hugetlb_handle_userfault(vma, mapping, idx,
>  						       flags, haddr,
>  						       VM_UFFD_MINOR);
>