Some Proxmox users reported an occasional assertion failure [0][1] in
busy VMs when using drive mirror with active mode. In particular, the
failure may occur for zero writes shorter than the job granularity:
> #0 0x00007b421154b507 in abort ()
> #1 0x00007b421154b420 in ?? ()
> #2 0x0000641c582e061f in bitmap_set (map=0x7b4204014e00, start=14, nr=-1)
> #3 0x0000641c58062824 in do_sync_target_write (job=0x641c7e73d1e0,
> method=MIRROR_METHOD_ZERO, offset=852480, bytes=4096, qiov=0x0, flags=0)
> #4 0x0000641c58062250 in bdrv_mirror_top_do_write (bs=0x641c7e62e1f0,
method=MIRROR_METHOD_ZERO, copy_to_target=true, offset=852480,
bytes=4096, qiov=0x0, flags=0)
> #5 0x0000641c58061f31 in bdrv_mirror_top_pwrite_zeroes (bs=0x641c7e62e1f0,
offset=852480, bytes=4096, flags=0)
The range for the dirty bitmap described by dirty_bitmap_offset and
dirty_bitmap_end is narrower than the original range and in fact,
dirty_bitmap_end might be smaller than dirty_bitmap_offset. There
already is a check for 'dirty_bitmap_offset < dirty_bitmap_end' before
resetting the dirty bitmap. Add such a check for setting the zero
bitmap too, which uses the same narrower range.
[0]: https://forum.proxmox.com/threads/177981/
[1]: https://bugzilla.proxmox.com/show_bug.cgi?id=7222
Cc: qemu-stable@nongnu.org
Fixes: 7e277545b9 ("mirror: Skip writing zeroes when target is already zero")
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20260112152544.261923-1-f.ebner@proxmox.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
4a7b1bd18d