From patchwork Mon Jan 22 16:01:26 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13525678 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 lists.gnu.org (lists.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 9B531C47DAF for ; Mon, 22 Jan 2024 16:02:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rRwk8-0001aW-6V; Mon, 22 Jan 2024 11:01:48 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rRwk4-0001W8-1y for qemu-devel@nongnu.org; Mon, 22 Jan 2024 11:01:44 -0500 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 1rRwk2-0004CE-Gk for qemu-devel@nongnu.org; Mon, 22 Jan 2024 11:01:43 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1705939301; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9eZYOBiyLtZMjq2yi8d9zHmoX+ctsJtlNfR3xYLfzKY=; b=UEVZxXcOwS+arC92C0WlVKlHrAvEczjCMxwr6o+D5fIVn/9WN3UCjQ+Dv11xyywZEe+L3R wXlyn2mwXJ2qFfZFsiVEwyI2a0tgrEquf2VESAq4THJ7bmy5dVlCvOKTaDy8tkkJj4rjeW SNLMC5DprNuurMKAVM9+sNmeEFj/iXg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-655-PtCncahCMqW2fSpv_o-Raw-1; Mon, 22 Jan 2024 11:01:35 -0500 X-MC-Unique: PtCncahCMqW2fSpv_o-Raw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6E87C85A5BC; Mon, 22 Jan 2024 16:01:34 +0000 (UTC) Received: from localhost (unknown [10.39.194.240]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DEDA1C060AF; Mon, 22 Jan 2024 16:01:32 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Hanna Reitz , Stefan Hajnoczi , Peter Maydell , qemu-block@nongnu.org, Fam Zheng , Kevin Wolf , Fiona Ebner , Vladimir Sementsov-Ogievskiy Subject: [PULL 2/2] block/io: clear BDRV_BLOCK_RECURSE flag after recursing in bdrv_co_block_status Date: Mon, 22 Jan 2024 11:01:26 -0500 Message-ID: <20240122160126.394141-3-stefanha@redhat.com> In-Reply-To: <20240122160126.394141-1-stefanha@redhat.com> References: <20240122160126.394141-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.289, 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_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: 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 From: Fiona Ebner Using fleecing backup like in [0] on a qcow2 image (with metadata preallocation) can lead to the following assertion failure: > bdrv_co_do_block_status: Assertion `!(ret & BDRV_BLOCK_ZERO)' failed. In the reproducer [0], it happens because the BDRV_BLOCK_RECURSE flag will be set by the qcow2 driver, so the caller will recursively check the file child. Then the BDRV_BLOCK_ZERO set too. Later up the call chain, in bdrv_co_do_block_status() for the snapshot-access driver, the assertion failure will happen, because both flags are set. To fix it, clear the recurse flag after the recursive check was done. In detail: > #0 qcow2_co_block_status Returns 0x45 = BDRV_BLOCK_RECURSE | BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID. > #1 bdrv_co_do_block_status Because of the data flag, bdrv_co_do_block_status() will now also set BDRV_BLOCK_ALLOCATED. Because of the recurse flag, bdrv_co_do_block_status() for the bdrv_file child will be called, which returns 0x16 = BDRV_BLOCK_ALLOCATED | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_ZERO. Now the return value inherits the zero flag. Returns 0x57 = BDRV_BLOCK_RECURSE | BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_ALLOCATED | BDRV_BLOCK_ZERO. > #2 bdrv_co_common_block_status_above > #3 bdrv_co_block_status_above > #4 bdrv_co_block_status > #5 cbw_co_snapshot_block_status > #6 bdrv_co_snapshot_block_status > #7 snapshot_access_co_block_status > #8 bdrv_co_do_block_status Return value is propagated all the way up to here, where the assertion failure happens, because BDRV_BLOCK_RECURSE and BDRV_BLOCK_ZERO are both set. > #9 bdrv_co_common_block_status_above > #10 bdrv_co_block_status_above > #11 block_copy_block_status > #12 block_copy_dirty_clusters > #13 block_copy_common > #14 block_copy_async_co_entry > #15 coroutine_trampoline [0]: > #!/bin/bash > rm /tmp/disk.qcow2 > ./qemu-img create /tmp/disk.qcow2 -o preallocation=metadata -f qcow2 1G > ./qemu-img create /tmp/fleecing.qcow2 -f qcow2 1G > ./qemu-img create /tmp/backup.qcow2 -f qcow2 1G > ./qemu-system-x86_64 --qmp stdio \ > --blockdev qcow2,node-name=node0,file.driver=file,file.filename=/tmp/disk.qcow2 \ > --blockdev qcow2,node-name=node1,file.driver=file,file.filename=/tmp/fleecing.qcow2 \ > --blockdev qcow2,node-name=node2,file.driver=file,file.filename=/tmp/backup.qcow2 \ > < {"execute": "qmp_capabilities"} > {"execute": "blockdev-add", "arguments": { "driver": "copy-before-write", "file": "node0", "target": "node1", "node-name": "node3" } } > {"execute": "blockdev-add", "arguments": { "driver": "snapshot-access", "file": "node3", "node-name": "snap0" } } > {"execute": "blockdev-backup", "arguments": { "device": "snap0", "target": "node1", "sync": "full", "job-id": "backup0" } } > EOF Signed-off-by: Fiona Ebner Reviewed-by: Vladimir Sementsov-Ogievskiy Message-id: 20240116154839.401030-1-f.ebner@proxmox.com Signed-off-by: Stefan Hajnoczi --- block/io.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/block/io.c b/block/io.c index 8fa7670571..33150c0359 100644 --- a/block/io.c +++ b/block/io.c @@ -2584,6 +2584,16 @@ bdrv_co_do_block_status(BlockDriverState *bs, bool want_zero, ret |= (ret2 & BDRV_BLOCK_ZERO); } } + + /* + * Now that the recursive search was done, clear the flag. Otherwise, + * with more complicated block graphs like snapshot-access -> + * copy-before-write -> qcow2, where the return value will be propagated + * further up to a parent bdrv_co_do_block_status() call, both the + * BDRV_BLOCK_RECURSE and BDRV_BLOCK_ZERO flags would be set, which is + * not allowed. + */ + ret &= ~BDRV_BLOCK_RECURSE; } out: