On Thu, Aug 22, 2013 at 05:48:24PM +0800, Wanpeng Li wrote:
> There is a race between hwpoison page and unpoison page, memory_failure
> set the page hwpoison and increase num_poisoned_pages without hold page
> lock, and one page count will be accounted against thp for num_poisoned_pages.
> However, unpoison can occur before memory_failure hold page lock and
> split transparent hugepage, unpoison will decrease num_poisoned_pages
> by 1 << compound_order since memory_failure has not yet split transparent
> hugepage with page lock held. That means we account one page for hwpoison
> and 1 << compound_order for unpoison. This patch fix it by decrease one
> account for num_poisoned_pages against no hugetlbfs pages case.
>
> Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
I think that a thp never becomes hwpoisoned without splitting, so "trying
to unpoison thp" never happens (I think that this implicit fact should be
commented somewhere or asserted with VM_BUG_ON().)
And nr_pages in unpoison_memory() can be greater than 1 for hugetlbfs page.
So does this patch break counting when unpoisoning free hugetlbfs pages?
Thanks,
Naoya Horiguchi
> ---
> mm/memory-failure.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 5092e06..6bfd51e 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1350,7 +1350,7 @@ int unpoison_memory(unsigned long pfn)
> return 0;
> }
> if (TestClearPageHWPoison(p))
> - atomic_long_sub(nr_pages, &num_poisoned_pages);
> + atomic_long_dec(&num_poisoned_pages);
> pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn);
> return 0;
> }
> --
> 1.8.1.2
>
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