g_disk_done() vs a destroyed disk

[Andriy Gapon]

I've seen a situation where g_disk_done() was called on a bio after the
corresponding disk had been already destroyed via g_disk_destroy().
That call resulted in a crash here:
	devstat_end_transaction_bio_bt(sc->dp->d_devstat, bp, &now);
because sc->dp was NULL.

Is it a bug that we do not check for dp being NULL (or dp->d_destroyed being
set) in g_disk_done() ?
Or is it a bug that a controller driver called biodone() for that bio having
earlier called disk_destroy() ?

Thanks!
-- 
Andriy Gapon