Re: [PATCH v3 2/3] mm/sparse: fix possible memory leak

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

On Mon, Jul 02, 2012 at 11:43:31AM +0200, Michal Hocko wrote:
>On Mon 02-07-12 17:28:56, Gavin Shan wrote:
>> 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.
>
>I would still like to hear how we can possibly race in this code path.
>I've thought that memory onlining is done from a single CPU.
>

Hi Michael, how about to use the following changelog? :-)

-----

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,
which is probablly caused by making online for multiple memory sections
that depend on same entry of array mem_section[] simultaneously from
different CPUs. The one that loses the race will leak the "section" that
sparse_index_alloc() allocated for it. This patch fixes that leak.

-----

Thanks,
Gavin

>> 
>> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
>> ---
>>  mm/sparse.c |   17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>> 
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index 781fa04..a6984d9 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -75,6 +75,20 @@ static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)
>>  	return section;
>>  }
>>  
>> +static inline void __meminit sparse_index_free(struct mem_section *section)
>> +{
>> +	unsigned long size = SECTIONS_PER_ROOT *
>> +			     sizeof(struct mem_section);
>> +
>> +	if (!section)
>> +		return;
>> +
>> +	if (slab_is_available())
>> +		kfree(section);
>> +	else
>> +		free_bootmem(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 +116,9 @@ 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);
>> +
>>  	return ret;
>>  }
>>  #else /* !SPARSEMEM_EXTREME */
>> -- 
>> 1.7.9.5
>> 
>> --
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>
>-- 
>Michal Hocko
>SUSE Labs
>SUSE LINUX s.r.o.
>Lihovarska 1060/12
>190 00 Praha 9    
>Czech Republic
>
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>To unsubscribe, send a message with 'unsubscribe linux-mm' in
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