From: Naoya Horiguchi <redacted>
Subject: mm, hwpoison: fix condition in free hugetlb page path

When a memory error hits a tail page of a free hugepage,
__page_handle_poison() is expected to be called to isolate the error in
4kB unit, but it's not called due to the outdated if-condition in
memory_failure_hugetlb().  This loses the chance to isolate the error in
the finer unit, so it's not optimal.  Drop the condition.

This "(p != head && TestSetPageHWPoison(head)" condition is based on the
old semantics of PageHWPoison on hugepage (where PG_hwpoison flag was set
on the subpage), so it's not necessray any more.  By getting to set
PG_hwpoison on head page for hugepages, concurrent error events on
different subpages in a single hugepage can be prevented by
TestSetPageHWPoison(head) at the beginning of memory_failure_hugetlb(). 
So dropping the condition should not reopen the race window originally
mentioned in commit b985194c8c0a ("hwpoison, hugetlb:
lock_page/unlock_page does not match for handling a free hugepage")

[naoya.horiguchi@linux.dev: fix "HardwareCorrupted" counter]
  Link: https://lkml.kernel.org/r/20211220084851.GA1460264@u2004
Link: https://lkml.kernel.org/r/20211210110208.879740-1-naoya.horiguchi@linux.dev
Signed-off-by: Naoya Horiguchi <redacted>
Reported-by: Fei Luo <redacted>
Reviewed-by: Mike Kravetz <redacted>
Cc: <redacted>	[5.14+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory-failure.c |   13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

--- a/mm/memory-failure.c~mm-hwpoison-fix-condition-in-free-hugetlb-page-path
+++ a/mm/memory-failure.c

@@ -1470,17 +1470,12 @@ static int memory_failure_hugetlb(unsign
 	if (!(flags & MF_COUNT_INCREASED)) {
 		res = get_hwpoison_page(p, flags);
 		if (!res) {
-			/*
-			 * Check "filter hit" and "race with other subpage."
-			 */
 			lock_page(head);
-			if (PageHWPoison(head)) {
-				if ((hwpoison_filter(p) && TestClearPageHWPoison(p))
-				    || (p != head && TestSetPageHWPoison(head))) {
+			if (hwpoison_filter(p)) {
+				if (TestClearPageHWPoison(head))
 					num_poisoned_pages_dec();
-					unlock_page(head);
-					return 0;
-				}
+				unlock_page(head);
+				return 0;
 			}
 			unlock_page(head);
 			res = MF_FAILED;

_