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.
The interface of soft-offlining is open for userspace, so this bug can
lead to DoS attack and should be fixed immedately.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
mm/memory-failure.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git v3.7-rc7.orig/mm/memory-failure.c v3.7-rc7/mm/memory-failure.c
index 8fe3640..e48e235 100644
--- v3.7-rc7.orig/mm/memory-failure.c
+++ v3.7-rc7/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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