[PATCH v3 4/8] mm/memory-failure.c: fix race with changing page more robustly

[Miaohe Lin]

We're only intended to deal with the non-Compound page after we split thp
in memory_failure. However, the page could have changed compound pages due
to race window. If this happens, we could retry once to hopefully handle
the page next round. Also remove unneeded orig_head. It's always equal to
the hpage. So we can use hpage directly and remove this redundant one.

Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 mm/memory-failure.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 7e205d91b2d7..2ca50cfa601f 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1690,7 +1690,6 @@ int memory_failure(unsigned long pfn, int flags)
 {
 	struct page *p;
 	struct page *hpage;
-	struct page *orig_head;
 	struct dev_pagemap *pgmap;
 	int res = 0;
 	unsigned long page_flags;
@@ -1736,7 +1735,7 @@ int memory_failure(unsigned long pfn, int flags)
 		goto unlock_mutex;
 	}
 
-	orig_head = hpage = compound_head(p);
+	hpage = compound_head(p);
 	num_poisoned_pages_inc();
 
 	/*
@@ -1817,10 +1816,21 @@ int memory_failure(unsigned long pfn, int flags)
 	lock_page(p);
 
 	/*
-	 * The page could have changed compound pages during the locking.
-	 * If this happens just bail out.
+	 * We're only intended to deal with the non-Compound page here.
+	 * However, the page could have changed compound pages due to
+	 * race window. If this happens, we could try again to hopefully
+	 * handle the page next round.
 	 */
-	if (PageCompound(p) && compound_head(p) != orig_head) {
+	if (PageCompound(p)) {
+		if (retry) {
+			if (TestClearPageHWPoison(p))
+				num_poisoned_pages_dec();
+			unlock_page(p);
+			put_page(p);
+			flags &= ~MF_COUNT_INCREASED;
+			retry = false;
+			goto try_again;
+		}
 		action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);
 		res = -EBUSY;
 		goto unlock_page;
-- 
2.23.0