Re: [PATCH 2/2] mm/hwpoison: fix refcount of THP head page in no-injection case

[Naoya Horiguchi]

On Mon, Aug 10, 2015 at 05:06:25PM +0800, Wanpeng Li wrote:
...
> >>>diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
> >>>index 5015679..c343a45 100644
> >>>--- a/mm/hwpoison-inject.c
> >>>+++ b/mm/hwpoison-inject.c
> >>>@@ -56,6 +56,8 @@ inject:
> >>>      return memory_failure(pfn, 18, MF_COUNT_INCREASED);
> >>>  put_out:
> >>>      put_page(p);
> >>>+    if (p != hpage)
> >>>+        put_page(hpage);
> >>Yes, we need this when we inject to a thp tail page and "goto put_out"
> >>is
> >>called. But it seems that this code can be called also when injecting
> >>error
> >>to a hugetlb tail page and hwpoison_filter() returns non-zero, which is
> >>not
> >>expected. Unfortunately simply doing like below
> >>
> >>+    if (!PageHuge(p) && p != hpage)
> >>+        put_page(hpage);
> >>
> >>doesn't work, because exisiting put_page(p) can release refcount of
> >>hugetlb
> >>tail page, while get_hwpoison_page() takes refcount of hugetlb head
> >>page.
> >>
> >>So I feel that we need put_hwpoison_page() to properly release the
> >>refcount
> >>taken by memory error handlers.
> >
> >Good point. I think I will continue to do it and will post it out soon. :)
> 
> How about something like this:
> 
> +void put_hwpoison_page(struct page *page)
> +{
> +       struct page *head = compound_head(page);
> +
> +       if (PageHuge(head))
> +               goto put_out;
> +
> +       if (PageTransHuge(head))
> +               if (page != head)
> +                       put_page(head);
> +
> +put_out:
> +       put_page(page);
> +       return;
> +}
> +

Looks good.

> Any comments are welcome, I can update the patch by myself. :)

Most of callsites of put_page() in memory_failure(), soft_offline_page(),
and unpoison_page() can be replaced with put_hwpoison_page().

Thanks,
Naoya Horiguchi--
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