From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 79FB3CD4851 for ; Tue, 12 May 2026 12:24:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wMm9E-0007Og-Nx; Tue, 12 May 2026 08:23:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wMm8i-0007NN-VJ for qemu-devel@nongnu.org; Tue, 12 May 2026 08:23:12 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wMm8b-0006w4-5y for qemu-devel@nongnu.org; Tue, 12 May 2026 08:23:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1778588578; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rmUszY8Ay3e5iEQfb45OQFt940K5N8zmKwgSlWjYZCM=; b=WFFbrWVrzLz3pCuppMhsGl6QlxJn3ypSyWLk3P4pBNGtTcMP8rKs1rizJURZbWKgV/HHOp XqEs3UDIU91S4ceJBrSU4/y5oiGwU51s4cqRC/MMb9Fjht2g33NkMM7XvpwL8EwzfkWBC2 hJGre/E7AG+WeGDennK6bTbdtv/O3XA= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-277-vWhkNvv5Nvmrs_h9Vaemjg-1; Tue, 12 May 2026 08:22:56 -0400 X-MC-Unique: vWhkNvv5Nvmrs_h9Vaemjg-1 X-Mimecast-MFC-AGG-ID: vWhkNvv5Nvmrs_h9Vaemjg_1778588575 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4EB361956095; Tue, 12 May 2026 12:22:55 +0000 (UTC) Received: from redhat.com (unknown [10.44.49.152]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8CE1118004A3; Tue, 12 May 2026 12:22:52 +0000 (UTC) Date: Tue, 12 May 2026 14:22:49 +0200 From: Kevin Wolf To: Fiona Ebner Cc: qemu-block@nongnu.org, hreitz@redhat.com, den@openvz.org, stefanha@redhat.com, qemu-stable@nongnu.org, qemu-devel@nongnu.org Subject: Re: [PATCH 3/4] qcow2: Fix corruption on discard during write with COW Message-ID: References: <20260427170520.101242-1-kwolf@redhat.com> <20260427170520.101242-4-kwolf@redhat.com> <76eb4371-8cfe-4d9f-870f-56c9a6dda334@proxmox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <76eb4371-8cfe-4d9f-870f-56c9a6dda334@proxmox.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 29.04.2026 um 17:28 hat Fiona Ebner geschrieben: > Am 27.04.26 um 7:04 PM schrieb Kevin Wolf: > > @@ -2000,6 +2028,15 @@ int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset, > > int64_t cleared; > > int ret; > > > > + /* > > + * If we're touching a cluster for which allocating writes are in flight, > > + * wait for them to complete to avoid conflicting metadata updates. > > + * > > + * We don't need to allocate a QCowL2Meta for the discard operation because > > + * s->lock is held for the duration of the whole operation. > > The caller in qcow2_make_empty() does not acquire s->lock AFAICS. Can > that be a problem? This is the case the comment inside wait_for_dependencies() is about: /* * Discard has some non-coroutine callers (creating internal snapshots and * make empty). They are calling from qemu-img or in a drained section, so * we know that no writes can be in progress. */ So it should be fine in practice because we know a bigger hammer is already in use for synchronisation. Kevin > > + */ > > + wait_for_dependencies(bs, offset, bytes); > > + > > /* Caller must pass aligned values, except at image end */ > > assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); > > assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||