linux-kernel - Re: [PATCH 1/2] memblock: add assertion for zero allocation size

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Message-ID: <CAE9FiQXSPHjRsCWcHpz7s1gQjNGuj5_X_YE2Ln=EA7_-Ka_cNg@mail.gmail.com>
Date:	Thu, 21 Feb 2013 11:27:16 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Zankel <chris@...kel.net>,
	Max Filippov <jcmvbkbc@...il.com>,
	Marc Gauthier <marc@...silica.com>, Tejun Heo <tj@...nel.org>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] memblock: add assertion for zero allocation size

[+Cc: hpa]

On Thu, Feb 21, 2013 at 10:39 AM, Vineet Gupta
<Vineet.Gupta1@...opsys.com> wrote:
> This came to light when calling memblock allocator from arc port (for
> copying flattended DT). If a "0" alignment is passed, the allocator
> round_up() call incorrectly rounds up the size to 0.
>
> round_up(num, alignto) => ((num - 1) | (alignto -1)) + 1
>
> While the obvious allocation failure causes kernel to panic, it is
> better to BUG_ON() if effective size for allocation (as passed by caller
> and/or computed after alignemtn rounding) is zero.

should we just make align to 1 instead of 0 ?

or BUG_ON(!align) instead?

>
> Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Yinghai Lu <yinghai@...nel.org>
> Cc: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  mm/memblock.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 1bcd9b9..32b36d0 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -824,6 +824,8 @@ static phys_addr_t __init memblock_alloc_base_nid(phys_addr_t size,
>         /* align @size to avoid excessive fragmentation on reserved array */
>         size = round_up(size, align);
>
> +       BUG_ON(!size);
> +
>         found = memblock_find_in_range_node(0, max_addr, size, align, nid);
>         if (found && !memblock_reserve(found, size))
>                 return found;
> --
> 1.7.4.1
>
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