On Tue, Nov 27, 2012 at 01:08:38PM -0800, Andi Kleen wrote:
> Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> writes:
>
> > When we try to soft-offline a thp tail page, put_page() is called on the
> > tail page unthinkingly and VM_BUG_ON is triggered in put_compound_page().
> > This patch splits thp before going into the main body of soft-offlining.
>
> Looks good.
>
> >
> > The interface of soft-offlining is open for userspace, so this bug can
> > lead to DoS attack and should be fixed immedately.
>
> The interface is root only and root can do everything anyways, so it's
> not really a security issue.
OK, this description had better not be here. I replace with attached one.
(.. and I forgot to disable suppress-cc for stable@xxxxxxxxxxxxxxx in
the initial post so did it now, sorry.)
---
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Date: Tue, 27 Nov 2012 15:38:23 -0500
Subject: [PATCH] mm, soft offline: split thp at the beginning of
soft_offline_page()
When we try to soft-offline a thp tail page, put_page() is called on the
tail page unthinkingly and VM_BUG_ON is triggered in put_compound_page().
This patch splits thp before going into the main body of soft-offlining.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
mm/memory-failure.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 8fe3640..e48e235 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1548,9 +1548,17 @@ int soft_offline_page(struct page *page, int flags)
{
int ret;
unsigned long pfn = page_to_pfn(page);
+ struct page *hpage = compound_trans_head(page);
if (PageHuge(page))
return soft_offline_huge_page(page, flags);
+ if (PageTransHuge(hpage)) {
+ if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
+ pr_info("soft offline: %#lx: failed to split THP\n",
+ pfn);
+ return -EBUSY;
+ }
+ }
ret = get_any_page(page, pfn, flags);
if (ret < 0)
--
1.7.11.7
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