[patch 5/9] mm, hwpoison: fix condition in free hugetlb page path

Andrew Morton
2021-12-25T05:12:49Z

From: Naoya Horiguchi <naoya.horiguchi@nec.com>
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4kB unit, but it's not called due to the outdated if-condition in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 <naoya.horiguchi@nec.com>
Reported-by: Fei Luo <luofei@unicloud.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: <stable@vger.kernel.org> [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;
_