[PATCH v1] mm, hwpoison: enable error handling on shmem thp

[Naoya Horiguchi <nao.horiguchi@gmail.com>]

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

Currently hwpoison code checks PageAnon() for thp and refuses to handle
errors on non-anonymous thps (just for historical reason).  We now
support non-anonymou thp like shmem one, so this patch suggests to enable
to handle shmem thps. Fortunately, we already have can_split_huge_page()
to check if a give thp is splittable, so this patch relies on it.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
---
 mm/memory-failure.c | 34 +++++++++-------------------------
 1 file changed, 9 insertions(+), 25 deletions(-)

diff --git v5.11-rc6/mm/memory-failure.c v5.11-rc6_patched/mm/memory-failure.c
index e9481632fcd1..8c1575de0507 100644
--- v5.11-rc6/mm/memory-failure.c
+++ v5.11-rc6_patched/mm/memory-failure.c
@@ -956,20 +956,6 @@ static int __get_hwpoison_page(struct page *page)
 {
 	struct page *head = compound_head(page);
 
-	if (!PageHuge(head) && PageTransHuge(head)) {
-		/*
-		 * Non anonymous thp exists only in allocation/free time. We
-		 * can't handle such a case correctly, so let's give it up.
-		 * This should be better than triggering BUG_ON when kernel
-		 * tries to touch the "partially handled" page.
-		 */
-		if (!PageAnon(head)) {
-			pr_err("Memory failure: %#lx: non anonymous thp\n",
-				page_to_pfn(page));
-			return 0;
-		}
-	}
-
 	if (get_page_unless_zero(head)) {
 		if (head == compound_head(page))
 			return 1;
@@ -1197,21 +1183,19 @@ static int identify_page_state(unsigned long pfn, struct page *p,
 
 static int try_to_split_thp_page(struct page *page, const char *msg)
 {
-	lock_page(page);
-	if (!PageAnon(page) || unlikely(split_huge_page(page))) {
-		unsigned long pfn = page_to_pfn(page);
+	struct page *head;
 
+	lock_page(page);
+	head = compound_head(page);
+	if (PageTransHuge(head) && can_split_huge_page(head, NULL) &&
+	    !split_huge_page(page)) {
 		unlock_page(page);
-		if (!PageAnon(page))
-			pr_info("%s: %#lx: non anonymous thp\n", msg, pfn);
-		else
-			pr_info("%s: %#lx: thp split failed\n", msg, pfn);
-		put_page(page);
-		return -EBUSY;
+		return 0;
 	}
+	pr_info("%s: %#lx: thp split failed\n", msg, page_to_pfn(page));
 	unlock_page(page);
-
-	return 0;
+	put_page(page);
+	return -EBUSY;
 }
 
 static int memory_failure_hugetlb(unsigned long pfn, int flags)
-- 
2.25.1