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: 40fd8683a22a ("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>

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index de88f33519c0d6398de8fcc06bfa82f2a477dd95..19e796d36a629147dd36217ecab34934300dc660 100644 (file)
--- 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);
        }