fix various bugs and issues with alarm(2)
1.  after 49/2 days, it is possible for a process at the head of the alarm
list clearing its alarm with alarm(0) to stop processing of the alarm list
for 49/2 days.

2.  after 49/2 days, it is possible for processes clearing their alarm with
alarm(0) to cause new timers to be inserted out-of-order.

3.  it is possible for alarms to be delivered to a different process if the alarm
kproc does not hold up-debug when checking the alarm.

Reference: /n/atom/patch/applied/alarm9
Date: Fri Jan  3 03:33:24 CET 2014
Signed-off-by: quanstro@quanstr.net

--- /sys/src/9/port/alarm.c	Fri Jan  3 03:30:39 2014
+++ /sys/src/9/port/alarm.c	Fri Jan  3 03:30:40 2014
@@ -16,20 +16,19 @@
 	for(;;){
 		now = MACHP(0)->ticks;
 		qlock(&alarms);
-		while((rp = alarms.head) && (long)(now - rp->alarm) >= 0){
-			if(rp->alarm != 0L){
-				if(canqlock(&rp->debug)){
-					if(!waserror()){
-						postnote(rp, 0, "alarm", NUser);
-						poperror();
-					}
-					qunlock(&rp->debug);
-					rp->alarm = 0L;
-				}else
-					break;
-			}
-			alarms.head = rp->palarm;
+		for(rp = alarms.head; rp != nil; rp = rp->palarm){
+			if(rp->alarm == 0)
+				continue;
+			if((long)(now - rp->alarm) < 0)
+				break;
+			if(canqlock(&rp->debug))
+				break;
+			if(rp->alarm != 0)
+				postnote(rp, 0, "alarm", NUser);
+			rp->alarm = 0;
+			qunlock(&rp->debug);
 		}
+		alarms.head = rp;
 		qunlock(&alarms);
 
 		sleep(&alarmr, return0, 0);
@@ -48,7 +47,8 @@
 	p = alarms.head;
 	now = MACHP(0)->ticks;
 
-	if(p != nil && (long)(now - p->alarm) >= 0)
+	if(p != nil)
+	if(p->alarm == 0 || (long)(now - p->alarm) >= 0)
 		wakeup(&alarmr);
 }
 
@@ -79,23 +79,16 @@
 		}
 		l = &f->palarm;
 	}
-
 	up->palarm = 0;
-	if(alarms.head) {
-		l = &alarms.head;
-		for(f = *l; f; f = f->palarm) {
-			if((long)(f->alarm - when) >= 0) {
-				up->palarm = f;
-				*l = up;
-				goto done;
-			}
-			l = &f->palarm;
-		}
-		*l = up;
+	l = &alarms.head;
+	for(f = *l; f != nil; f = f->palarm) {
+		time = f->alarm;
+		if(time != 0 && (long)(time - when) >= 0)
+			break;
+		l = &f->palarm;
 	}
-	else
-		alarms.head = up;
-done:
+	up->palarm = f;
+	*l = up;
 	up->alarm = when;
 	qunlock(&alarms);
 
--- /sys/src/9/port/devproc.c	Fri Jan  3 03:30:42 2014
+++ /sys/src/9/port/devproc.c	Fri Jan  3 03:30:44 2014
@@ -1116,9 +1116,10 @@
 		}
 		t = proctab(0);
 		for(et = t+conf.nproc; t < et; t++) {
-			if(t->state == Dead)
+			if(t->state == Dead || t->kp)
 				continue;
 			if(id == t->noteid) {
+				nonone(t);
 				if(strcmp(p->user, t->user) != 0)
 					error(Eperm);
 				p->noteid = id;