x86/HPET: deal with event having expired while interrupt was masked

x86/HPET: deal with event having expired while interrupt was masked

Commit 2d8a282 ("x86/HPET: fix FSB interrupt masking") may cause the
HPET event to occur while its interrupt is masked. In that case we need
to "manually" deliver the event.

Unfortunately this requires the locking to be changed: For one, it was
always bogus for handle_hpet_broadcast() to use spin_unlock_irq() - the
function is being called from an interrupt handler, and hence shouldn't
blindly re-enable interrupts (this should be left up to the generic
interrupt handling code). And with the event handler wanting to acquire
the lock for two of its code regions, we must not enter it with the
lock already held. Hence move the locking into
hpet_{attach,detach}_channel(), permitting the lock to be dropped by
set_channel_irq_affinity() (which is a tail call of those functions).

Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Sander Eikelenboom <linux@eikelenboom.it>
Acked-by: Keir Fraser <keir@xen.org>