From patchwork Wed Feb 6 12:32:02 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: 218632 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 A58C32C02B4 for ; Thu, 7 Feb 2013 01:12:23 +1100 (EST) Received: from localhost ([::1]:56994 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1U35jZ-0003sm-Os for incoming@patchwork.ozlabs.org; Wed, 06 Feb 2013 09:12:21 -0500 Received: from eggs.gnu.org ([208.118.235.92]:56142) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1U34CQ-0007wP-NY for qemu-devel@nongnu.org; Wed, 06 Feb 2013 07:34:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1U34CN-0005O6-6P for qemu-devel@nongnu.org; Wed, 06 Feb 2013 07:34:02 -0500 Received: from nodalink.pck.nerim.net ([62.212.105.220]:43697 helo=paradis.irqsave.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1U34CM-0005Nn-TN for qemu-devel@nongnu.org; Wed, 06 Feb 2013 07:33:59 -0500 Received: by paradis.irqsave.net (Postfix, from userid 1002) id 458B5874327; Wed, 6 Feb 2013 13:33:58 +0100 (CET) Received: from localhost.localdomain (unknown [192.168.77.1]) by paradis.irqsave.net (Postfix) with ESMTP id 3213C87433C; Wed, 6 Feb 2013 13:31:21 +0100 (CET) From: =?UTF-8?q?Beno=C3=AEt=20Canet?= To: qemu-devel@nongnu.org Date: Wed, 6 Feb 2013 13:32:02 +0100 Message-Id: <1360153926-9492-30-git-send-email-benoit@irqsave.net> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <1360153926-9492-1-git-send-email-benoit@irqsave.net> References: <1360153926-9492-1-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, =?UTF-8?q?Beno=C3=AEt=20Canet?= , stefanha@redhat.com Subject: [Qemu-devel] [RFC V6 29/33] 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