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author | Fiona Ebner <f.ebner@proxmox.com> | 2024-01-16 16:48:39 +0100 |
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committer | Stefan Hajnoczi <stefanha@redhat.com> | 2024-01-22 11:00:12 -0500 |
commit | 8a9be7992426c8920d4178e7dca59306a18c7a3a (patch) | |
tree | 0f732c85ee69afacade9bf0b35d3bbf209511b28 /block | |
parent | d9945ccda08ef83b09ac7725b6ee2d1959f2c0c0 (diff) | |
download | qemu-8a9be7992426c8920d4178e7dca59306a18c7a3a.zip qemu-8a9be7992426c8920d4178e7dca59306a18c7a3a.tar.gz qemu-8a9be7992426c8920d4178e7dca59306a18c7a3a.tar.bz2 |
block/io: clear BDRV_BLOCK_RECURSE flag after recursing in bdrv_co_block_status
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>
Message-id: 20240116154839.401030-1-f.ebner@proxmox.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'block')
-rw-r--r-- | block/io.c | 10 |
1 files changed, 10 insertions, 0 deletions
@@ -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: |