linux-kernel - Re: [PATCH v2 1/2] memblock: add assertion for zero allocation alignment

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Message-ID: <CAE9FiQV20uj_kOViCOd4gdPFuAf28fEbjhGCrzNogQWx5T3+zg@mail.gmail.com>
Date:	Thu, 21 Feb 2013 12:31:34 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.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 v2 1/2] memblock: add assertion for zero allocation alignment

On Thu, Feb 21, 2013 at 12:10 PM, 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 warn the caller to fix the code.
>
> Tejun suggested that instead of BUG_ON(!align) - which might be
> ineffective due to pending console init and such, it is better to
> WARN_ON, and continue the boot with a reasonable default align.
>
> Caller passing @size need not be handled similarly as the subsequent
> panic will indicate that anyhow.
>
> 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 |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 1bcd9b9..f3804bd 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -824,6 +824,9 @@ 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);
>
> +       if (WARN_ON(!align))
> +               align = __alignof__(long long);
> +

the checking should be put before round_up?

>         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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