From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756085AbbCCMC7 (ORCPT ); Tue, 3 Mar 2015 07:02:59 -0500 Received: from mail-pd0-f176.google.com ([209.85.192.176]:32868 "EHLO mail-pd0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751468AbbCCMC5 (ORCPT ); Tue, 3 Mar 2015 07:02:57 -0500 From: Leon Yu To: Andrew Morton , Konstantin Khlebnikov , Rik van Riel , Michal Hocko Cc: Leon Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] mm: fix anon_vma->degree underflow in anon_vma endless growing prevention Date: Tue, 3 Mar 2015 20:02:15 +0800 Message-Id: <1425384142-5064-1-git-send-email-chianglungyu@gmail.com> X-Mailer: git-send-email 2.1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I have constantly stumbled upon "kernel BUG at mm/rmap.c:399!" after upgrading to 3.19 and had no luck with 4.0-rc1 neither. So, after looking into new logic introduced by commit 7a3ef208e662, ("mm: prevent endless growth of anon_vma hierarchy"), I found chances are that unlink_anon_vmas() is called without incrementing dst->anon_vma->degree in anon_vma_clone() due to allocation failure. If dst->anon_vma is not NULL in error path, its degree will be incorrectly decremented in unlink_anon_vmas() and eventually underflow when exiting as a result of another call to unlink_anon_vmas(). That's how "kernel BUG at mm/rmap.c:399!" is triggered for me. This patch fixes the underflow by dropping dst->anon_vma when allocation fails. It's safe to do so regardless of original value of dst->anon_vma because dst->anon_vma doesn't have valid meaning if anon_vma_clone() fails. Besides, callers don't care dst->anon_vma in such case neither. Signed-off-by: Leon Yu Fixes: 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") Cc: stable@vger.kernel.org # v3.19 --- mm/rmap.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/rmap.c b/mm/rmap.c index 5e3e090..bed3cf2 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -287,6 +287,13 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) return 0; enomem_failure: + /* + * dst->anon_vma is dropped here otherwise its degree can be incorrectly + * decremented in unlink_anon_vmas(). + * We can safely do this because calllers of anon_vma_clone() wouldn't + * care dst->anon_vma if anon_vma_clone() failed. + */ + dst->anon_vma = NULL; unlink_anon_vmas(dst); return -ENOMEM; } -- 2.3.1