linux-kernel - Re: [PATCH] mm: memory-failure: fix potential page refcnt leak in memory

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Date:   Mon, 3 Jul 2023 15:37:13 +0900
From:   Naoya Horiguchi <naoya.horiguchi@...ux.dev>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, naoya.horiguchi@....com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memory-failure: fix potential page refcnt leak in
 memory_failure()

On Sat, Jul 01, 2023 at 03:28:37PM +0800, Miaohe Lin wrote:
> put_ref_page() is not called to drop extra refcnt when comes from madvise
> in the case pfn is valid but pgmap is NULL leading to page refcnt leak.

Is this test scenario realistic one?  I don't think that we can call madvise() for
such a device memory page.  If this is the case, this issue can be thought as
potentioal one (so no need to send to stable). 

> 
> Fixes: 1e8aaedb182d ("mm,memory_failure: always pin the page in madvise_inject_error")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Anyway, the patch looks good to me. Thanks you.

Acked-by: Naoya Horiguchi <naoya.horiguchi@....com>

> ---
>  mm/memory-failure.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e245191e6b04..65e2d4c5b50d 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2080,8 +2080,6 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  {
>  	int rc = -ENXIO;
>  
> -	put_ref_page(pfn, flags);
> -
>  	/* device metadata space is not recoverable */
>  	if (!pgmap_pfn_valid(pgmap, pfn))
>  		goto out;
> @@ -2157,6 +2155,7 @@ int memory_failure(unsigned long pfn, int flags)
>  
>  		if (pfn_valid(pfn)) {
>  			pgmap = get_dev_pagemap(pfn, NULL);
> +			put_ref_page(pfn, flags);
>  			if (pgmap) {
>  				res = memory_failure_dev_pagemap(pfn, flags,
>  								 pgmap);
> -- 
> 2.33.0
> 
> 
>