From nobody Tue Nov 26 16:44:19 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1706464155865678.8219204854939; Sun, 28 Jan 2024 09:49:15 -0800 (PST) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rU9GR-0005x5-Vt; Sun, 28 Jan 2024 12:48:16 -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 1rU9GB-0005rL-SW; Sun, 28 Jan 2024 12:48:01 -0500 Received: from isrv.corpit.ru ([86.62.121.231]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rU9G9-0000FX-K3; Sun, 28 Jan 2024 12:47:59 -0500 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id D4E0B480DD; Sun, 28 Jan 2024 20:48:41 +0300 (MSK) Received: from tls.msk.ru (mjt.wg.tls.msk.ru [192.168.177.130]) by tsrv.corpit.ru (Postfix) with SMTP id 17D306D506; Sun, 28 Jan 2024 20:47:50 +0300 (MSK) Received: (nullmailer pid 811308 invoked by uid 1000); Sun, 28 Jan 2024 17:47:47 -0000 From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Fiona Ebner , Vladimir Sementsov-Ogievskiy , Stefan Hajnoczi , Michael Tokarev Subject: [Stable-7.2.9 23/30] block/io: clear BDRV_BLOCK_RECURSE flag after recursing in bdrv_co_block_status Date: Sun, 28 Jan 2024 20:47:36 +0300 Message-Id: <20240128174747.811264-3-mjt@tls.msk.ru> X-Mailer: git-send-email 2.39.2 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1706464158695100003 Content-Type: text/plain; charset="utf-8" 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 =3D 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 =3D BDRV_BLOCK_ALLOCATED | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_ZERO. Now the return value inherits the zero flag. Returns 0x57 =3D 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=3Dmetadata -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=3Dnode0,file.driver=3Dfile,file.filename=3D/tm= p/disk.qcow2 \ > --blockdev qcow2,node-name=3Dnode1,file.driver=3Dfile,file.filename=3D/tm= p/fleecing.qcow2 \ > --blockdev qcow2,node-name=3Dnode2,file.driver=3Dfile,file.filename=3D/tm= p/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 (cherry picked from commit 8a9be7992426c8920d4178e7dca59306a18c7a3a) Signed-off-by: Michael Tokarev diff --git a/block/io.c b/block/io.c index bbaa0d1b2d..4589a58917 100644 --- a/block/io.c +++ b/block/io.c @@ -2595,6 +2595,16 @@ static int coroutine_fn bdrv_co_block_status(BlockDr= iverState *bs, ret |=3D (ret2 & BDRV_BLOCK_ZERO); } } + + /* + * Now that the recursive search was done, clear the flag. Otherwi= se, + * with more complicated block graphs like snapshot-access -> + * copy-before-write -> qcow2, where the return value will be prop= agated + * further up to a parent bdrv_co_do_block_status() call, both the + * BDRV_BLOCK_RECURSE and BDRV_BLOCK_ZERO flags would be set, whic= h is + * not allowed. + */ + ret &=3D ~BDRV_BLOCK_RECURSE; } =20 out: --=20 2.39.2