[PATCH v1 4/5] mm, hwpoison: skip raw hwpoison page in freeing 1GB hugepage

[Naoya Horiguchi]

From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>

Currently if memory_failure() (modified to remove blocking code) is called
on a page in some 1GB hugepage, memory error handling returns failure and
the raw error page gets into undesirable state.  The impact is small in
production systems (just leaked single 4kB page), but this limits the test
efficiency because unpoison doesn't work for it.  So we can no longer
create 1GB hugepage on the 1GB physical address range with such hwpoison
pages, that could be an issue in testing on small systems.

When a hwpoison page in a 1GB hugepage is handled, it's caught by the
PageHWPoison check in free_pages_prepare() because the hugepage is broken
down into raw error page and order is 0:

        if (unlikely(PageHWPoison(page)) && !order) {
                ...
                return false;
        }

Then, the page is not sent to buddy and the page refcount is left 0.

Originally this check is supposed to work when the error page is freed from
page_handle_poison() (that is called from soft-offline), but now we are
opening another path to call it, so the callers of __page_handle_poison()
need to handle the case by considering the return value 0 as success. Then
page refcount for hwpoison is properly incremented and now unpoison works.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
---
 mm/memory-failure.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index f149a7864c81..babeb34f7477 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1043,7 +1043,6 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 		res = truncate_error_page(hpage, page_to_pfn(p), mapping);
 		unlock_page(hpage);
 	} else {
-		res = MF_FAILED;
 		unlock_page(hpage);
 		/*
 		 * migration entry prevents later access on error anonymous
@@ -1051,9 +1050,11 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 		 * save healthy subpages.
 		 */
 		put_page(hpage);
-		if (__page_handle_poison(p) > 0) {
+		if (__page_handle_poison(p) >= 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
+		} else {
+			res = MF_FAILED;
 		}
 	}
 
@@ -1601,9 +1602,11 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 	 */
 	if (res == 0) {
 		unlock_page(head);
-		if (__page_handle_poison(p) > 0) {
+		if (__page_handle_poison(p) >= 0) {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
+		} else {
+			res = MF_FAILED;
 		}
 		action_result(pfn, MF_MSG_FREE_HUGE, res);
 		return res == MF_RECOVERED ? 0 : -EBUSY;
-- 
2.25.1