linux-kernel - Re: [PATCH 04/14] mm/hmm: hmm_pfns_bad() was accessing wrong struct

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Date:   Fri, 16 Mar 2018 19:04:08 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     <jglisse@...hat.com>, <linux-mm@...ck.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        Evgeny Baskakov <ebaskakov@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Mark Hairgrove <mhairgrove@...dia.com>
Subject: Re: [PATCH 04/14] mm/hmm: hmm_pfns_bad() was accessing wrong struct

On 03/16/2018 12:14 PM, jglisse@...hat.com wrote:
> From: Jérôme Glisse <jglisse@...hat.com>
> 
> The private field of mm_walk struct point to an hmm_vma_walk struct and
> not to the hmm_range struct desired. Fix to get proper struct pointer.
> 
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> Cc: stable@...r.kernel.org
> Cc: Evgeny Baskakov <ebaskakov@...dia.com>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: Mark Hairgrove <mhairgrove@...dia.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> ---
>  mm/hmm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 6088fa6ed137..64d9e7dae712 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -293,7 +293,8 @@ static int hmm_pfns_bad(unsigned long addr,
>  			unsigned long end,
>  			struct mm_walk *walk)
>  {
> -	struct hmm_range *range = walk->private;
> +	struct hmm_vma_walk *hmm_vma_walk = walk->private;
> +	struct hmm_range *range = hmm_vma_walk->range;
>  	hmm_pfn_t *pfns = range->pfns;
>  	unsigned long i;
>  

This fix looks good. I also checked the other uses of walk->private, of course, 
but it was only this one that was wrong.

I think this patch also belongs in -stable, because it is a simple bug fix.

For the description, well...actually, because ->range is the first element in
struct hmm_vma_walk, you probably end up with the same pointer value, both
before and after this fix. So maybe there are no symptoms to see. Maybe that's
an argument for *not* putting it in -stable, too. I'll leave that question
to more experienced people.

Either way, you can add: 

Reviewed by: John Hubbard <jhubbard@...dia.com>

thanks,
-- 
John Hubbard
NVIDIA