panic in biodone2

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

A few days ago I burnt a DVD while mounting a USB mass media device,
copying data to it and unmounting it.

umass0 at uhub2 port 2 configuration 1 interface 0
umass0: Meizu   Electronics MiniPlayer, rev 2.00/1.00, addr 5
umass0: using SCSI over Bulk-Only
scsibus0 at umass0: 2 targets, 1 lun per target
sd0 at scsibus0 target 0 lun 0: <Meizu, MiniPlayer, 1.00> disk
removable
sd0: 7820 MB, 7840 cyl, 16 head, 32 sec, 512 bytes/sect x 16015360
sectors
umass0: Phase Error, residue = 0
sd0: cache synchronization failed
[this always happens with this device, see PR 40442]
umass0: at uhub2 port 2 (addr 5) disconnected
sd0: detached
scsibus0: detached
umass0: detached

A short time later the machine paniced:
panic: biodone2 already
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip ffffffff80175b85 cs 8 rflags 246 cr2
ffff800049218000 cpl 0 rsp ffff8000495f62f0

Is this a side effect of the cache sync error?
These are separate busses (sd@umass vs. cd@viaide).
After reboot, without any USB messing, I could write a DVD without the
panic.
The kernel was 5.99.7/amd64/Feb 16 08:16.
 Thomas