The only way I know of to call xpt_async with AC_ADVINFO_CHANGED is when the
ses(4) driver sets the physical path of a device. And since that only happens
when a device is inserted (or a SES device changes its configuration, which
never happens on my hardware), symptoms will only be visible if the enc_daemon
thread is running slow. Otherwise it will set the physical path before the
device finishes creating all of its devnodes on startup. And the only way I
know to slow down enc_daemon is to attach a large number of devices at the same
time.
For example, without this patch, attaching 95 disks at once resulted in all of
them getting physical path device nodes for their da devices, but only two
got physical path device nodes for their pass devices.