mm/memory-failure: give up error handling for non-tail-refcounted thp

"non anonymous thp" case is still racy with freeing thp, which causes
panic due to put_page() for refcount-0 page.  It seems that closing up
this race might be hard (and/or not worth doing,) so let's give up the
error handling for this case.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Dean Nelson <dnelson@redhat.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
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 f72d2fad0b90c1a26878ea2438520b9ab94538b7..cd985530f10239d4118f5170684a8482e810ebc2 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -909,6 +909,18 @@ int get_hwpoison_page(struct page *page)
         * directly for tail pages.
         */
        if (PageTransHuge(head)) {
+               /*
+                * Non anonymous thp exists only in allocation/free time. We
+                * can't handle such a case correctly, so let's give it up.
+                * This should be better than triggering BUG_ON when kernel
+                * tries to touch the "partially handled" page.
+                */
+               if (!PageAnon(head)) {
+                       pr_err("MCE: %#lx: non anonymous thp\n",
+                               page_to_pfn(page));
+                       return 0;
+               }
+
                if (get_page_unless_zero(head)) {
                        if (PageTail(page))
                                get_page(page);
@@ -1134,15 +1146,6 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
        }
 
        if (!PageHuge(p) && PageTransHuge(hpage)) {
-               if (!PageAnon(hpage)) {
-                       pr_err("MCE: %#lx: non anonymous thp\n", pfn);
-                       if (TestClearPageHWPoison(p))
-                               atomic_long_sub(nr_pages, &num_poisoned_pages);
-                       put_page(p);
-                       if (p != hpage)
-                               put_page(hpage);
-                       return -EBUSY;
-               }
                if (unlikely(split_huge_page(hpage))) {
                        pr_err("MCE: %#lx: thp split failed\n", pfn);
                        if (TestClearPageHWPoison(p))