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Subject[PATCH 3.2 20/79] mm/memory-failure.c: recheck PageHuge() after hugetlb page migrate successfully
3.2.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jianguo Wu <wujianguo@huawei.com>

commit a49ecbcd7b0d5a1cda7d60e03df402dd0ef76ac8 upstream.

After a successful hugetlb page migration by soft offline, the source
page will either be freed into hugepage_freelists or buddy(over-commit
page). If page is in buddy, page_hstate(page) will be NULL. It will
hit a NULL pointer dereference in dequeue_hwpoisoned_huge_page().

BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
IP: [<ffffffff81163761>] dequeue_hwpoisoned_huge_page+0x131/0x1d0
PGD c23762067 PUD c24be2067 PMD 0
Oops: 0000 [#1] SMP

So check PageHuge(page) after call migrate_pages() successfully.

Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
Tested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[wujg: backport to 3.4:
- adjust context
- s/num_poisoned_pages/mce_bad_pages/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
mm/memory-failure.c | 16 ++++++++++++----
1 files changed, 12 insertions(+), 4 deletions(-)

--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1441,10 +1441,18 @@ static int soft_offline_huge_page(struct
return ret;
}
done:
- if (!PageHWPoison(hpage))
- atomic_long_add(1 << compound_trans_order(hpage), &mce_bad_pages);
- set_page_hwpoison_huge_page(hpage);
- dequeue_hwpoisoned_huge_page(hpage);
+ /* overcommit hugetlb page will be freed to buddy */
+ if (PageHuge(hpage)) {
+ if (!PageHWPoison(hpage))
+ atomic_long_add(1 << compound_trans_order(hpage),
+ &mce_bad_pages);
+ set_page_hwpoison_huge_page(hpage);
+ dequeue_hwpoisoned_huge_page(hpage);
+ } else {
+ SetPageHWPoison(page);
+ atomic_long_inc(&mce_bad_pages);
+ }
+
/* keep elevated page count for bad page */
return ret;
}


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