mm: hwpoison: fix thp split handling in memory_failure()

When memory_failure() runs on a thp tail page after pmd is split, we
trigger the following VM_BUG_ON_PAGE():

   page:ffffd7cd819b0040 count:0 mapcount:0 mapping:         (null) index:0x1
   flags: 0x1fffc000400000(hwpoison)
   page dumped because: VM_BUG_ON_PAGE(!page_count(p))
   ------------[ cut here ]------------
   kernel BUG at /src/linux-dev/mm/memory-failure.c:1132!

memory_failure() passed refcount and page lock from tail page to head
page, which is not needed because we can pass any subpage to
split_huge_page().

Fixes: 61f5d698cc97 ("mm: re-enable THP")
Link: http://lkml.kernel.org/r/1477961577-7183-1-git-send-email-n-horiguchi@ah.jp.nec.com
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: <stable@vger.kernel.org>	[4.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 7 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index de88f33519c0..19e796d36a62 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1112,10 +1112,10 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
         }
 
         if (!PageHuge(p) && PageTransHuge(hpage)) {
-                lock_page(hpage);
-                if (!PageAnon(hpage) || unlikely(split_huge_page(hpage))) {
-                        unlock_page(hpage);
-                        if (!PageAnon(hpage))
+                lock_page(p);
+                if (!PageAnon(p) || unlikely(split_huge_page(p))) {
+                        unlock_page(p);
+                        if (!PageAnon(p))
                                 pr_err("Memory failure: %#lx: non anonymous thp\n",
                                         pfn);
                         else
@@ -1126,9 +1126,7 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
                         put_hwpoison_page(p);
                         return -EBUSY;
                 }
-                unlock_page(hpage);
-                get_hwpoison_page(p);
-                put_hwpoison_page(hpage);
+                unlock_page(p);
                 VM_BUG_ON_PAGE(!page_count(p), p);
                 hpage = compound_head(p);
         }