+ mm-hwpoison-fix-condition-in-free-hugetlb-page-path.patch added to -mm tree

The patch titled
     Subject: mm, hwpoison: fix condition in free hugetlb page path
has been added to the -mm tree.  Its filename is
     mm-hwpoison-fix-condition-in-free-hugetlb-page-path.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-hwpoison-fix-condition-in-free-hugetlb-page-path.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-hwpoison-fix-condition-in-free-hugetlb-page-path.patch

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------------------------------------------------------
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4kB unit, but it's not called due to the outdated if-condition in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")

Link: https://lkml.kernel.org/r/20211210110208.879740-1-naoya.horiguchi@linux.dev
Signed-off-by: Naoya Horiguchi <redacted>
Reported-by: Fei Luo <redacted>
Cc: <redacted>	[5.14+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory-failure.c |   21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

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

@@ -1470,24 +1470,17 @@ 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;
-			if (__page_handle_poison(p)) {
-				page_ref_inc(p);
-				res = MF_RECOVERED;
-			}
+			res = MF_RECOVERED;
+			if (!page_handle_poison(p, true, false))
+				res = MF_FAILED;
 			action_result(pfn, MF_MSG_FREE_HUGE, res);
 			return res == MF_RECOVERED ? 0 : -EBUSY;
 		} else if (res < 0) {

_

Patches currently in -mm which might be from naoya.horiguchi@nec.com are

mm-hwpoison-fix-condition-in-free-hugetlb-page-path.patch
mm-hwpoison-mf_mutex-for-soft-offline-and-unpoison.patch
mm-hwpoison-remove-mf_msg_buddy_2nd-and-mf_msg_poisoned_huge.patch
mm-hwpoison-fix-unpoison_memory.patch