From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752480AbbAKNyO (ORCPT ); Sun, 11 Jan 2015 08:54:14 -0500 Received: from mail-lb0-f174.google.com ([209.85.217.174]:58507 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752340AbbAKNyL (ORCPT ); Sun, 11 Jan 2015 08:54:11 -0500 Subject: [PATCH] mm: fix corner case in anon_vma endless growing prevention From: Konstantin Khlebnikov To: linux-mm@kvack.org, Andrew Morton , Linus Torvalds , linux-kernel@vger.kernel.org Cc: Rik van Riel , "Elifaz, Dana" , "Bridgman, John" , Daniel Forrest , Chris Clayton , Oded Gabbay , Michal Hocko Date: Sun, 11 Jan 2015 16:54:06 +0300 Message-ID: <20150111135406.13266.42007.stgit@zurg> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Fix for BUG_ON(anon_vma->degree) splashes in unlink_anon_vmas() ("kernel BUG at mm/rmap.c:399!"). Anon_vma_clone() is usually called for a copy of source vma in destination argument. If source vma has anon_vma it should be already in dst->anon_vma. NULL in dst->anon_vma is used as a sign that it's called from anon_vma_fork(). In this case anon_vma_clone() finds anon_vma for reusing. Vma_adjust() calls it differently and this breaks anon_vma reusing logic: anon_vma_clone() links vma to old anon_vma and updates degree counters but vma_adjust() overrides vma->anon_vma right after that. As a result final unlink_anon_vmas() decrements degree for wrong anon_vma. This patch assigns ->anon_vma before calling anon_vma_clone(). Signed-off-by: Konstantin Khlebnikov Fixes: 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") Tested-by: Chris Clayton Tested-by: Oded Gabbay Cc: Daniel Forrest Cc: Michal Hocko Cc: Rik van Riel --- mm/mmap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 7b36aa7..12616c5 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -778,10 +778,12 @@ again: remove_next = 1 + (end > next->vm_end); if (exporter && exporter->anon_vma && !importer->anon_vma) { int error; + importer->anon_vma = exporter->anon_vma; error = anon_vma_clone(importer, exporter); - if (error) + if (error) { + importer->anon_vma = NULL; return error; - importer->anon_vma = exporter->anon_vma; + } } }