On Sat 23-06-12 23:52:54, 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 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?
> 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.
> +
> 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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