From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758690Ab3JOLIr (ORCPT ); Tue, 15 Oct 2013 07:08:47 -0400 Received: from mail-pb0-f42.google.com ([209.85.160.42]:62049 "EHLO mail-pb0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758628Ab3JOLIq (ORCPT ); Tue, 15 Oct 2013 07:08:46 -0400 Date: Tue, 15 Oct 2013 04:08:28 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Andrea Arcangeli , David Rientjes , "Kirill A. Shutemov" , Naoya Horiguchi , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: mm: fix BUG in __split_huge_page_pmd Message-ID: User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Occasionally we hit the BUG_ON(pmd_trans_huge(*pmd)) at the end of __split_huge_page_pmd(): seen when doing madvise(,,MADV_DONTNEED). It's invalid: we don't always have down_write of mmap_sem there: a racing do_huge_pmd_wp_page() might have copied-on-write to another huge page before our split_huge_page() got the anon_vma lock. Forget the BUG_ON, just go back and try again if this happens. Signed-off-by: Hugh Dickins Cc: stable@vger.kernel.org --- mm/huge_memory.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- 3.12-rc5/mm/huge_memory.c 2013-09-16 17:37:56.811072270 -0700 +++ linux/mm/huge_memory.c 2013-10-15 03:40:02.044138488 -0700 @@ -2697,6 +2697,7 @@ void __split_huge_page_pmd(struct vm_are mmun_start = haddr; mmun_end = haddr + HPAGE_PMD_SIZE; +again: mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); spin_lock(&mm->page_table_lock); if (unlikely(!pmd_trans_huge(*pmd))) { @@ -2719,7 +2720,14 @@ void __split_huge_page_pmd(struct vm_are split_huge_page(page); put_page(page); - BUG_ON(pmd_trans_huge(*pmd)); + + /* + * We don't always have down_write of mmap_sem here: a racing + * do_huge_pmd_wp_page() might have copied-on-write to another + * huge page before our split_huge_page() got the anon_vma lock. + */ + if (unlikely(pmd_trans_huge(*pmd))) + goto again; } void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,