[PATCH] hwpoison: fix oops on ksm pages

[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@tiscali.co.uk>
---
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))

Re: [PATCH] hwpoison: fix oops on ksm pages

[Andi Kleen]

On Tue, Oct 13, 2009 at 03:02:11PM +0100, Hugh Dickins wrote:
> 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.

Thanks, Hugh. I'm curious: did this come out of code review or
did you actually run into that?

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.

Re: [PATCH] hwpoison: fix oops on ksm pages

[Hugh Dickins]

On Tue, 13 Oct 2009, Andi Kleen wrote:
> On Tue, Oct 13, 2009 at 03:02:11PM +0100, Hugh Dickins wrote:
> > 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.
> 
> Thanks, Hugh. I'm curious: did this come out of code review or
> did you actually run into that?

Just out of code review: well, that's too fancy a name for it, I merely
remembered that I hadn't looked at ksm/hwpoison interoperabilty, so did
so just now.  After looking at the code, I did then try MADV_HWPOISON on
a MADV_MERGEABLE area, to check that the problem and the fix were real.

Hugh

[PATCH] HWPOISON: fix oops on ksm pages

[Andi Kleen]

From: Hugh Dickins <hugh.dickins@tiscali.co.uk>

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@tiscali.co.uk>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 mm/memory-failure.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index e17ec3f..e354b9f 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -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>
@@ -644,7 +645,7 @@ static void hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	int i;
 	int kill = 1;
 
-	if (PageReserved(p) || PageCompound(p) || PageSlab(p))
+	if (PageReserved(p) || PageCompound(p) || PageSlab(p) || PageKsm(p))
 		return;
 
 	/*
-- 
1.6.0.2