From: Fiona Ebner <f.ebner@proxmox.com>
To: pve-devel@lists.proxmox.com
Subject: [pve-devel] [PATCH qemu 03/13] block/io: clear BDRV_BLOCK_RECURSE flag after recursing in bdrv_co_block_status
Date: Thu, 25 Jan 2024 15:41:39 +0100 [thread overview]
Message-ID: <20240125144149.216064-4-f.ebner@proxmox.com> (raw)
In-Reply-To: <20240125144149.216064-1-f.ebner@proxmox.com>
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 \
> <<EOF
> {"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 <f.ebner@proxmox.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
Can be added as an extra/ patch.
block/io.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/block/io.c b/block/io.c
index 63f7b3ad3e..24a3c84c93 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2589,6 +2589,16 @@ bdrv_co_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:
--
2.39.2
next prev parent reply other threads:[~2024-01-25 14:41 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-25 14:41 [pve-devel] [RFC qemu/guest-common/manager/qemu-server/docs 00/13] fix #4136: implement backup fleecing Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [PATCH qemu 01/13] backup: factor out gathering device info into helper Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [PATCH qemu 02/13] backup: get device info: code cleanup Fiona Ebner
2024-01-25 14:41 ` Fiona Ebner [this message]
2024-01-25 14:41 ` [pve-devel] [RFC qemu 04/13] block/copy-before-write: create block_copy bitmap in filter node Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [RFC qemu 05/13] qapi: blockdev-backup: add discard-source parameter Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [HACK qemu 06/13] block/{copy-before-write, snapshot-access}: implement bdrv_co_get_info driver callback Fiona Ebner
2024-01-29 14:35 ` Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [HACK qemu 07/13] block/block-copy: always consider source cluster size too Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [RFC qemu 08/13] PVE backup: add fleecing option Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [RFC guest-common 09/13] vzdump: schema: add fleecing property string Fiona Ebner
2024-01-29 15:41 ` Fiona Ebner
2024-01-30 14:03 ` DERUMIER, Alexandre
2024-02-01 8:28 ` Fiona Ebner
2024-02-01 12:39 ` DERUMIER, Alexandre
2024-02-01 13:11 ` Fiona Ebner
2024-02-01 13:20 ` DERUMIER, Alexandre
2024-02-01 13:27 ` Fiona Ebner
2024-02-01 21:33 ` DERUMIER, Alexandre
2024-02-02 8:30 ` Fiona Ebner
2024-02-01 13:30 ` Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [RFC manager 10/13] vzdump: handle new 'fleecing' " Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [RFC qemu-server 11/13] backup: disk info: also keep track of size Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [RFC qemu-server 12/13] backup: implement fleecing option Fiona Ebner
2024-01-29 15:28 ` Fiona Ebner
2024-01-25 14:41 ` [pve-devel] [RFC docs 13/13] vzdump: add section about backup fleecing Fiona Ebner
2024-01-25 16:13 ` Dietmar Maurer
2024-01-25 16:41 ` DERUMIER, Alexandre
2024-01-25 18:18 ` Dietmar Maurer
2024-01-26 8:39 ` Fiona Ebner
2024-01-25 16:02 ` [pve-devel] [RFC qemu/guest-common/manager/qemu-server/docs 00/13] fix #4136: implement " DERUMIER, Alexandre
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20240125144149.216064-4-f.ebner@proxmox.com \
--to=f.ebner@proxmox.com \
--cc=pve-devel@lists.proxmox.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox