Re: [PATCH v2 2/3] mm/sparse: fix possible memory leak

[Gavin Shan <shangw@linux.vnet.ibm.com>]

On Thu, Jun 28, 2012 at 02:57:42PM +0200, Michal Hocko wrote:
>On Thu 28-06-12 00:36:07, Gavin Shan wrote:
>> With CONFIG_SPARSEMEM_EXTREME, the root memory section descriptors
>> are allocated by slab or bootmem allocator. Also, the descriptors
>> might have been allocated and initialized during the hotplug path.
>> However, the memory chunk allocated in current implementation wouldn't
>> be put into the available pool if that has been allocated. The situation
>> will lead to memory leak.
>> 
>> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
>> Reviewed-by: Michal Hocko <mhocko@suse.cz>
>
>And again!
>To quote my answers to this patch in previous run:
>"
>I am not saying the bug is not real. It is just that the changelog
>doesn's say how the bug is hit, who is affected and when it has been
>introduced. These is essential for stable.
>"
>
>Does this sound like Reviewed-by? Hell no!
>

Ok. I won't do this again wrongly.

>This changelog btw. doesn't say this either!
>

Here's the changelog that Dave suggested. I just copy & paste it.

--

sparse_index_init() is designed to be safe if two copies of it race.  It
uses "index_init_lock" to ensure that, even in the case of a race, only
one CPU will manage to do:

        mem_section[root] = section;

However, in the case where two copies of sparse_index_init() _do_ race,
the one that loses the race will leak the "section" that
sparse_index_alloc() allocated for it.  This patch fixes that leak.

--

Thanks,
Gavin

>> ---
>>  mm/sparse.c |   19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>> 
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index 781fa04..a803599 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -75,6 +75,22 @@ static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)
>>  	return section;
>>  }
>>  
>> +static void noinline __init_refok sparse_index_free(struct mem_section *section,
>> +						    int nid)
>> +{
>> +	unsigned long size = SECTIONS_PER_ROOT *
>> +			     sizeof(struct mem_section);
>> +
>> +	if (!section)
>> +		return;
>> +
>> +	if (slab_is_available())
>> +		kfree(section);
>> +	else
>> +		free_bootmem_node(NODE_DATA(nid),
>> +			virt_to_phys(section), size);
>> +}
>> +
>>  static int __meminit sparse_index_init(unsigned long section_nr, int nid)
>>  {
>>  	static DEFINE_SPINLOCK(index_init_lock);
>> @@ -102,6 +118,9 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
>>  	mem_section[root] = section;
>>  out:
>>  	spin_unlock(&index_init_lock);
>> +	if (ret)
>> +		sparse_index_free(section, nid);
>> +
>>  	return ret;
>>  }
>>  #else /* !SPARSEMEM_EXTREME */
>> -- 
>> 1.7.9.5
>> 
>
>-- 
>Michal Hocko
>SUSE Labs
>SUSE LINUX s.r.o.
>Lihovarska 1060/12
>190 00 Praha 9    
>Czech Republic
>
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