From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f170.google.com (mail-pd0-f170.google.com [209.85.192.170]) by kanga.kvack.org (Postfix) with ESMTP id ADA496B0038 for ; Tue, 3 Mar 2015 07:02:57 -0500 (EST) Received: by pdjg10 with SMTP id g10so48021606pdj.1 for ; Tue, 03 Mar 2015 04:02:57 -0800 (PST) Received: from mail-pd0-x231.google.com (mail-pd0-x231.google.com. [2607:f8b0:400e:c02::231]) by mx.google.com with ESMTPS id os1si803692pac.67.2015.03.03.04.02.56 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 03 Mar 2015 04:02:57 -0800 (PST) Received: by pdjg10 with SMTP id g10so48021511pdj.1 for ; Tue, 03 Mar 2015 04:02:56 -0800 (PST) From: Leon Yu 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org