[PATCH] mm/memory-failure.c: recheck PageHuge() after hugetlb pagemigrate successfull

[Jianguo Wu]

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().

[  890.677918] BUG: unable to handle kernel NULL pointer dereference at
 0000000000000058
[  890.685741] IP: [<ffffffff81163761>]
dequeue_hwpoisoned_huge_page+0x131/0x1d0
[  890.692861] PGD c23762067 PUD c24be2067 PMD 0
[  890.697314] Oops: 0000 [#1] SMP

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

Signed-off-by: Jianguo Wu <wujianguo@xxxxxxxxxx>
---
 mm/memory-failure.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index b7c1716..e5567f2 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1471,7 +1471,8 @@ static int get_any_page(struct page *page, unsigned long pfn, int flags)
 
 static int soft_offline_huge_page(struct page *page, int flags)
 {
-	int ret;
+	int ret, i;
+	unsigned long nr_pages;
 	unsigned long pfn = page_to_pfn(page);
 	struct page *hpage = compound_head(page);
 	LIST_HEAD(pagelist);
@@ -1489,6 +1490,8 @@ static int soft_offline_huge_page(struct page *page, int flags)
 	}
 	unlock_page(hpage);
 
+	nr_pages = 1 << compound_order(hpage);
+
 	/* Keep page count to indicate a given hugepage is isolated. */
 	list_move(&hpage->lru, &pagelist);
 	ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL,
@@ -1505,10 +1508,16 @@ static int soft_offline_huge_page(struct page *page, int flags)
 		if (ret > 0)
 			ret = -EIO;
 	} else {
-		set_page_hwpoison_huge_page(hpage);
-		dequeue_hwpoisoned_huge_page(hpage);
-		atomic_long_add(1 << compound_order(hpage),
-				&num_poisoned_pages);
+		/* over-commit hugetlb page will be freed into buddy */
+		if (PageHuge(page)) {
+			set_page_hwpoison_huge_page(hpage);
+			dequeue_hwpoisoned_huge_page(hpage);
+		} else {
+			for (i = 0; i < nr_pages; i++)
+				SetPageHWPoison(hpage + i);
+		}
+
+		atomic_long_add(nr_pages, &num_poisoned_pages);
 	}
 	return ret;
 }
-- 
1.8.2.2


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