>> 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@xxxxxxxxxxxxxxxxxx>
>> ---
>> 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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>> see: http://www.linux-mm.org/ .
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>
>--
>Michal Hocko
>SUSE Labs
>SUSE LINUX s.r.o.
>Lihovarska 1060/12
>190 00 Praha 9
>Czech Republic
>
>--
>To unsubscribe, send a message with 'unsubscribe linux-mm' in
>the body to majordomo@xxxxxxxxx. For more info on Linux MM,
>see: http://www.linux-mm.org/ .
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>
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