[PATCH] hwpoison: fix oops on ksm pages

[Hugh Dickins]

Memory failure on a KSM page currently oopses on its NULL anon_vma in
page_lock_anon_vma(): that may not be much worse than the consequence
of ignoring it, but it is better to be consistent with how ZERO_PAGE
and hugetlb pages and other awkward cases are treated.  Just skip it.

Signed-off-by: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
---
We could fix it for 2.6.32 at the KSM end, by putting a dummy anon_vma
pointer in there; but that would get harder next time, when KSM will
put a pointer to something else there (and I'm not currently planning
to do any work to open that up to memory_failure).  So I would prefer
this simple PageKsm test, until the other exceptions are handled.

 mm/memory-failure.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- 2.6.32-rc4/mm/memory-failure.c	2009-09-28 00:28:41.000000000 +0100
+++ linux/mm/memory-failure.c	2009-10-13 14:09:12.000000000 +0100
@@ -35,6 +35,7 @@
 #include <linux/mm.h>
 #include <linux/page-flags.h>
 #include <linux/sched.h>
+#include <linux/ksm.h>
 #include <linux/rmap.h>
 #include <linux/pagemap.h>
 #include <linux/swap.h>
@@ -661,7 +662,7 @@ static void hwpoison_user_mappings(struc
 	int i;
 	int kill = 1;
 
-	if (PageReserved(p) || PageCompound(p) || PageSlab(p))
+	if (PageReserved(p) || PageCompound(p) || PageSlab(p) || PageKsm(p))
 		return;
 
 	if (!PageLRU(p))
--
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