From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f179.google.com (mail-we0-f179.google.com [74.125.82.179]) by kanga.kvack.org (Postfix) with ESMTP id 751906B009E for ; Sun, 11 Jan 2015 10:05:05 -0500 (EST) Received: by mail-we0-f179.google.com with SMTP id q59so15221543wes.10 for ; Sun, 11 Jan 2015 07:05:05 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id l4si8975166wiw.19.2015.01.11.07.05.04 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 11 Jan 2015 07:05:04 -0800 (PST) Message-ID: <54B2911D.4050904@suse.cz> Date: Sun, 11 Jan 2015 16:05:01 +0100 From: Vlastimil Babka MIME-Version: 1.0 Subject: Re: [PATCH] mm: fix corner case in anon_vma endless growing prevention References: <20150111135406.13266.42007.stgit@zurg> In-Reply-To: <20150111135406.13266.42007.stgit@zurg> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov , 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 On 01/11/2015 02:54 PM, Konstantin Khlebnikov wrote: > 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 Acked-by: Vlastimil Babka > --- > 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; > + } > } > } > > > -- > 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 > -- 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