Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755231AbbBQCcB (ORCPT ); Mon, 16 Feb 2015 21:32:01 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:33768 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752002AbbBQBu5 (ORCPT ); Mon, 16 Feb 2015 20:50:57 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Daniel Forrest" , "Vlastimil Babka" , "Rik van Riel" , "Linus Torvalds" , "Michal Hocko" , "Konstantin Khlebnikov" Date: Tue, 17 Feb 2015 01:46:53 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 104/152] mm: fix corner case in anon_vma endless growing prevention In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2420 Lines: 63 3.2.67-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Konstantin Khlebnikov commit b800c91a0517071156e772d4fb329ad33590da62 upstream. Fix for BUG_ON(anon_vma->degree) splashes in unlink_anon_vmas() ("kernel BUG at mm/rmap.c:399!") caused by commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") 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 Reported-and-tested-by: Chris Clayton Reported-and-tested-by: Oded Gabbay Reported-and-tested-by: Chih-Wei Huang Acked-by: Rik van Riel Acked-by: Vlastimil Babka Cc: Daniel Forrest Cc: Michal Hocko Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: vma_adjust() didn't use a variable to propagate the error code from anon_vma_clone(); change that at the same time] Signed-off-by: Ben Hutchings --- --- a/mm/mmap.c +++ b/mm/mmap.c @@ -537,9 +537,14 @@ again: remove_next = 1 + (end > next-> * shrinking vma had, to cover any anon pages imported. */ if (exporter && exporter->anon_vma && !importer->anon_vma) { - if (anon_vma_clone(importer, exporter)) - return -ENOMEM; + int error; + importer->anon_vma = exporter->anon_vma; + error = anon_vma_clone(importer, exporter); + if (error) { + importer->anon_vma = NULL; + return error; + } } } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/