From: Ivan Kokshaysky <ink@jurassic.park.msu.ru>

When CONFIG_SMP is not set, spinlock_t is an empty structure, so its
address has arbitrary alignment.

The prefetch instructions with unaligned address don't have visible side
effects on alphas with SRM console (except performance degradation) - the
PALcode handles unaligned traps caused by prefetch instructions internally.
However, on old AlphaBIOS/MILO boxes unaligned prefetch leads to unhandled
alignment trap and kernel panic.