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bh=9eZYOBiyLtZMjq2yi8d9zHmoX+ctsJtlNfR3xYLfzKY=; b=UEVZxXcOwS+arC92C0WlVKlHrAvEczjCMxwr6o+D5fIVn/9WN3UCjQ+Dv11xyywZEe+L3R wXlyn2mwXJ2qFfZFsiVEwyI2a0tgrEquf2VESAq4THJ7bmy5dVlCvOKTaDy8tkkJj4rjeW SNLMC5DprNuurMKAVM9+sNmeEFj/iXg= X-MC-Unique: PtCncahCMqW2fSpv_o-Raw-1 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 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 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=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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1705939338439100005 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 --- 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 w= ant_zero, 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 2.43.0