linux-kernel - Re: + memblock-add-assertion-for-zero-allocation-alignment.patch added to -mm tree

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Date:	Wed, 6 Mar 2013 16:07:20 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	akpm@...ux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	mm-commits@...r.kernel.org, Vineet.Gupta1@...opsys.com,
	liwanp@...ux.vnet.ibm.com, mingo@...nel.org, tj@...nel.org,
	vgupta@...opsys.com
Subject: Re: + memblock-add-assertion-for-zero-allocation-alignment.patch
 added to -mm tree

On Wed, Mar 6, 2013 at 2:44 PM,  <akpm@...ux-foundation.org> wrote:
> ------------------------------------------------------
> From: Vineet Gupta <Vineet.Gupta1@...opsys.com>
> Subject: memblock: add assertion for zero allocation alignment
>
> 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: Yinghai Lu <yinghai@...nel.org>
> Cc: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Acked-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>
>  mm/memblock.c |    3 +++
>  1 file changed, 3 insertions(+)
>
> diff -puN mm/memblock.c~memblock-add-assertion-for-zero-allocation-alignment mm/memblock.c
> --- a/mm/memblock.c~memblock-add-assertion-for-zero-allocation-alignment
> +++ a/mm/memblock.c
> @@ -771,6 +771,9 @@ static phys_addr_t __init memblock_alloc
>  {
>         phys_addr_t found;
>
> +       if (WARN_ON(!align))
> +               align = __alignof__(long long);
> +
>         /* align @size to avoid excessive fragmentation on reserved array */
>         size = round_up(size, align);

Hi, Peter,

Do you agree that we should check align in round_up()?

Thanks

Yinghai
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