As a temporary hack, turn off deferred preemptions that are the result of

a fast interrupt handler doing an swi_sched().  This fixed the lockups I
saw on my laptop when using xmms in KDE and on rwatson's MySQL benchmarks
on SMP.  This will eventually be removed and/or modified when I figure out
what the root cause is and fix that.

sys/alpha/alpha/interrupt.c

@@ -435,6 +435,8 @@ alpha_dispatch_intr(void *frame, unsigned long vector)
 	if ((ih->ih_flags & IH_FAST) != 0) {
 		critical_enter();
 		ih->ih_handler(ih->ih_argument);
+		/* XXX */
+		td->td_pflags &= ~TDP_OWEPREEMPT;
 		critical_exit();
 		return;
 	}

sys/amd64/amd64/intr_machdep.c

@@ -204,6 +204,8 @@ intr_execute_handlers(struct intsrc *isrc, struct intrframe *iframe)
 		}
 		isrc->is_pic->pic_eoi_source(isrc);
 		error = 0;
+		/* XXX */
+		td->td_pflags &= ~TDP_OWEPREEMPT;
 		critical_exit();
 	} else {
 		/*

sys/i386/i386/intr_machdep.c

@@ -204,6 +204,8 @@ intr_execute_handlers(struct intsrc *isrc, struct intrframe *iframe)
 		}
 		isrc->is_pic->pic_eoi_source(isrc);
 		error = 0;
+		/* XXX */
+		td->td_pflags &= ~TDP_OWEPREEMPT;
 		critical_exit();
 	} else {
 		/*