[PATCH] hwpoison: Fix race with changing page during offlining v2

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>

When a hwpoison page is locked it could change state
due to parallel modifications.  Check after the lock
if the page is still the same compound page.

[v2: Removed earlier non LRU check which should be already
covered elsewhere]

Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 mm/memory-failure.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index cd8989c..99e5077 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1168,6 +1168,16 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	lock_page(hpage);
 
 	/*
+	 * The page could have changed compound pages during the locking.
+	 * If this happens just bail out.
+	 */
+	if (compound_head(p) != hpage) {
+		action_result(pfn, "different compound page after locking", IGNORED);
+		res = -EBUSY;
+		goto out;
+	}
+
+	/*
 	 * We use page flags to determine what action should be taken, but
 	 * the flags can be modified by the error containment action.  One
 	 * example is an mlocked page, where PG_mlocked is cleared by
-- 
1.9.3

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