linux-kernel - Re: [PATCH 01/10] mm/mmap: Replace SHM_HUGE_MASK with MAP_HUGE_MASK inside mmap

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Date:	Wed, 13 Apr 2016 09:54:17 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, hughd@...gle.com,
	kirill@...temov.name, n-horiguchi@...jp.nec.com,
	akpm@...ux-foundation.org, mgorman@...hsingularity.net,
	dave.hansen@...el.com, aneesh.kumar@...ux.vnet.ibm.com,
	mpe@...erman.id.au
Subject: Re: [PATCH 01/10] mm/mmap: Replace SHM_HUGE_MASK with MAP_HUGE_MASK
 inside mmap_pgoff

On Thu 07-04-16 11:07:35, Anshuman Khandual wrote:
> The commit 091d0d55b286 ("shm: fix null pointer deref when userspace
> specifies invalid hugepage size") had replaced MAP_HUGE_MASK with
> SHM_HUGE_MASK. Though both of them contain the same numeric value of
> 0x3f, MAP_HUGE_MASK flag sounds more appropriate than the other one
> in the context. Hence change it back.

Yes, SHM_HUGE_MASK mixing with MAP_HUGE_SHIFT is not only misleading
it might bite us later should any of the two change.

> 
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/mmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index bd2e1a53..7d730a4 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1315,7 +1315,7 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
>  		struct user_struct *user = NULL;
>  		struct hstate *hs;
>  
> -		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & SHM_HUGE_MASK);
> +		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
>  		if (!hs)
>  			return -EINVAL;
>  
> -- 
> 2.1.0
> 
> --
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-- 
Michal Hocko
SUSE Labs