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

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Date:	Fri, 22 Feb 2013 01:03:41 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	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

On Friday 22 February 2013 12:57 AM, Yinghai Lu wrote:
> [+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 ?

Where - you mean if user passes 0, just make it 1. Nah - it's better to complain
and get the call site fixed !

> or BUG_ON(!align) instead?

That could be done too but you would also need BUG_ON(!size) - to catch another
API abuse.
BUG_ON(!size) however catches both the cases.


>
>> 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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