From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f42.google.com (mail-la0-f42.google.com [209.85.215.42]) by kanga.kvack.org (Postfix) with ESMTP id C1DC86B009A for ; Sun, 11 Jan 2015 08:54:10 -0500 (EST) Received: by mail-la0-f42.google.com with SMTP id gd6so20752972lab.1 for ; Sun, 11 Jan 2015 05:54:10 -0800 (PST) Received: from mail-lb0-x232.google.com (mail-lb0-x232.google.com. [2a00:1450:4010:c04::232]) by mx.google.com with ESMTPS id dd11si13280967lac.130.2015.01.11.05.54.09 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 11 Jan 2015 05:54:09 -0800 (PST) Received: by mail-lb0-f178.google.com with SMTP id u14so14175389lbd.9 for ; Sun, 11 Jan 2015 05:54:09 -0800 (PST) Subject: [PATCH] mm: fix corner case in anon_vma endless growing prevention From: Konstantin Khlebnikov Date: Sun, 11 Jan 2015 16:54:06 +0300 Message-ID: <20150111135406.13266.42007.stgit@zurg> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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; + } } } -- 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