From patchwork Wed Jan 16 16:24:49 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: =?utf-8?q?Beno=C3=AEt_Canet?= X-Patchwork-Id: 212803 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 272EB2C0084 for ; Thu, 17 Jan 2013 03:27:54 +1100 (EST) Received: from localhost ([::1]:37462 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TvVqC-0004Cg-6P for incoming@patchwork.ozlabs.org; Wed, 16 Jan 2013 11:27:52 -0500 Received: from eggs.gnu.org ([208.118.235.92]:41519) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TvVpc-0003d6-FX for qemu-devel@nongnu.org; Wed, 16 Jan 2013 11:27:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TvVpa-0007IW-1W for qemu-devel@nongnu.org; Wed, 16 Jan 2013 11:27:16 -0500 Received: from nodalink.pck.nerim.net ([62.212.105.220]:43276 helo=paradis.irqsave.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TvVpZ-0007IN-QQ for qemu-devel@nongnu.org; Wed, 16 Jan 2013 11:27:13 -0500 Received: by paradis.irqsave.net (Postfix, from userid 1002) id 4305C874328; Wed, 16 Jan 2013 17:58:50 +0100 (CET) Received: from localhost.localdomain (unknown [192.168.77.1]) by paradis.irqsave.net (Postfix) with ESMTP id 54120874335; Wed, 16 Jan 2013 17:56:05 +0100 (CET) From: =?UTF-8?q?Beno=C3=AEt=20Canet?= To: qemu-devel@nongnu.org Date: Wed, 16 Jan 2013 17:24:49 +0100 Message-Id: <1358353497-5292-29-git-send-email-benoit@irqsave.net> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <1358353497-5292-1-git-send-email-benoit@irqsave.net> References: <1358353497-5292-1-git-send-email-benoit@irqsave.net> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 62.212.105.220 Cc: kwolf@redhat.com, pbonzini@redhat.com, =?UTF-8?q?Beno=C3=AEt=20Canet?= , stefanha@redhat.com Subject: [Qemu-devel] [RFC V5 28/36] qcow2: Do not overwrite existing entries with QCOW_OFLAG_COPIED. X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org In the case of a race condition between two writes a l2 entry can be written without QCOW_OFLAG_COPIED before the first write fill it. This patch simply check if the l2 entry has the correct offset without QCOW_OFLAG_COPIED and do nothing. Signed-off-by: Benoit Canet --- block/qcow2-cluster.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index fedcf57..c016e85 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -763,6 +763,11 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m) for (i = 0; i < m->nb_clusters; i++) { uint64_t flags = 0; uint64_t offset = cluster_offset + (i << s->cluster_bits); + + if (be64_to_cpu(l2_table[l2_index + i]) == offset) { + continue; + } + /* if two concurrent writes happen to the same unallocated cluster * each write allocates separate cluster and writes data concurrently. * The first one to complete updates l2 table with pointer to its