Re: [PATCH 3/5] mm/sparse: fix possible memory leak

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

>> 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 by others. However, the
>> memory chunk allocated in current implementation wouldn't be put
>> into the available pool if others have allocated memory chunk for
>> that.
>
>Who is others? I assume that we can race in hotplug because other than
>that this is an early initialization code. How can others race?
>

I'm sorry that I don't have the real bug against the issue. I just
catch it when reading the source code :-)

I do agree with you that the trace is possiblly introduced by the
hotplug case.

>> The patch introduces addtional function sparse_index_free() to
>> deallocate the memory chunk if the root memory section descriptor
>> has been initialized by others.
>
>The fix itself looks correct but I do not see how this happens...
>
>> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
>> ---
>>  mm/sparse.c |   19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>> 
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index ce50c8b..bae8f2d 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -86,6 +86,22 @@ 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);
>> @@ -113,6 +129,9 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
>>  	mem_section[root] = section;
>>  out:
>>  	spin_unlock(&index_init_lock);
>> +	if (ret == -EEXIST)
>> +		sparse_index_free(section, nid);
>
>Maybe a generic if (ret) would be more appropriate.
>

I will do it in next revision :-)

Thanks,
Gavin

>> +
>>  	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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