[PATCH 1/4] mm/memory-failure.c: fix race with changing page compound again

[Miaohe Lin <linmiaohe@huawei.com>]

There is a race window where we got the compound_head, the hugetlb page
could be freed to buddy, or even changed to another compound page just
before we try to get hwpoison page. If this happens, just bail out.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/memory-failure.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 5444a8ef4867..0d7c58340a98 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1534,6 +1534,17 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
 	}
 
 	lock_page(head);
+
+	/**
+	 * The page could have changed compound pages due to race window.
+	 * If this happens just bail out.
+	 */
+	if (!PageHuge(p) || compound_head(p) != head) {
+		action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);
+		res = -EBUSY;
+		goto out;
+	}
+
 	page_flags = head->flags;
 
 	if (hwpoison_filter(p)) {
-- 
2.23.0