From 7fd7a34974cdd9475f88cb4bd7b5594d214e5fe3 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Thu, 23 May 1996 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1996-05-23

---
 carrera/dat.h  |  1 -
 pc/dat.h       |  1 -
 port/proc.c    | 22 ++++++++------------
 port/taslock.c | 56 +++++++++++++-------------------------------------
 power/dat.h    |  1 -
 5 files changed, 22 insertions(+), 59 deletions(-)

diff --git a/carrera/dat.h b/carrera/dat.h
index d285b53735cdaa3ecec03b63f9d5d4e1479d7b2e..e4dffff10d14c50ece09aaf70e20da9462bb8885 100644
--- a/carrera/dat.h
+++ b/carrera/dat.h
@@ -27,7 +27,6 @@ struct Lock
 	ulong	sr;
 	ulong	pc;
 	ulong	pid;
-	int	pri;
 };
 
 struct Label
diff --git a/pc/dat.h b/pc/dat.h
index 22795973d5a0171b66ec0b108177a9a8bbd97fec..9d978318a6cf857cebd489e6b743b1f40ca756bc 100644
--- a/pc/dat.h
+++ b/pc/dat.h
@@ -30,7 +30,6 @@ struct Lock
 	ulong	sr;
 	ulong	pc;
 	ulong	pid;
-	int	pri;
 };
 
 struct Label
diff --git a/port/proc.c b/port/proc.c
index c0b1e1a1095987015a700544cf68a8d058ec4ded..c2331679f966346cf1e8fdc46c3c44a507ad90d4 100644
--- a/port/proc.c
+++ b/port/proc.c
@@ -130,21 +130,11 @@ enum
 void
 ready(Proc *p)
 {
-	int s, pri, base;
+	int s, pri;
 	Schedq *rq;
 
 	s = splhi();
 
-	/*
-	 *  This interacts with code in taslock().  The intent is to keep the
-	 *  priority of a process trying for a lock lower than the process holding
-	 *  the lock.
-	 */
-	if(p->lockpri)
-		base = p->lockpri;
-	else
-		base = p->basepri;
-
 	/* history counts */
 	if(p->state == Running){
 		p->rt++;
@@ -154,15 +144,19 @@ ready(Proc *p)
 		p->rt = 0;
 		pri = p->art/Squantum;
 	}
-	pri = base - pri;
+	pri = p->basepri - pri;
 	if(pri < 0)
 		pri = 0;
 
 	/* the only intersection between the classes is at PriNormal */
-	if(pri < PriNormal && base > PriNormal)
+	if(pri < PriNormal && p->basepri > PriNormal)
 		pri = PriNormal;
-	p->priority = pri;
 
+	/* hack for livelocks due to priority */
+	if(p->lockpri)
+		pri = 0;
+
+	p->priority = pri;
 	rq = &runq[p->priority];
 
 	lock(runq);
diff --git a/port/taslock.c b/port/taslock.c
index 789ed0859c3f19860746a8cc5851fa918131dad3..dc2b8b6836b171fdcbef2f4c77984450d3d47547 100644
--- a/port/taslock.c
+++ b/port/taslock.c
@@ -11,59 +11,41 @@ lockloop(Lock *l, ulong pc)
 	print("lock loop key 0x%lux pc 0x%lux held by pc 0x%lux proc %d\n",
 		l->key, pc, l->pc, l->pid);
 	dumpaproc(up);
-}
 
-#define LOCKLOOP 100000000	/* to detect a lock loop */
-#define SPINLOOP 10000000	/* to keep tas's off the bus */
+	/* lower priority till we get the lock */
+	if(up && up->state == Running && (getstatus()&IE)){
+		up->lockpri = 1;
+		sched();
+	}
+}
 
 void
 lock(Lock *l)
 {
-	int i, pri, spins;
+	int i;
 	ulong pc, pid;
 
 	pc = getcallerpc(l);
-	if(up){
-		pid = up->pid;
-		pri = up->priority;
-	} else {
-		pid = 0;
-		pri = 0;
-	}
+	pid = up ? up->pid : 0;
 
-	/* quick try, it might work */
 	if(tas(&l->key) == 0){
 		l->pc = pc;
 		l->pid = pid;
-		l->pri = pri;
 		return;
 	}
 
-	spins = 0;
 	for(;;){
 		i = 0;
 		while(l->key)
-			if(i++ > SPINLOOP){
-				/* look for lock loops */
-				if(spins++ > LOCKLOOP/SPINLOOP){
-					spins = 0;
-					lockloop(l, pc);
-				}
-
-				/* possible priority inversion, try switching priority */
-				if(up && up->state == Running)
-				if(getstatus()&IE) {
-print("priority inversion\n");
-					up->lockpri = l->pri;
-					sched();
-				}
+			if(i++ > 100000000){
+				i = 0;
+				lockloop(l, pc);
 			}
-
 		if(tas(&l->key) == 0){
 			l->pc = pc;
 			l->pid = pid;
-			l->pri = pri;
-			up->lockpri = 0;
+			if(up)
+				up->lockpri = 0;
 			return;
 		}
 	}
@@ -83,7 +65,6 @@ ilock(Lock *l)
 		l->sr = x;
 		l->pc = pc;
 		l->pid = pid;
-		l->pri = 0;
 		return;
 	}
 
@@ -94,7 +75,6 @@ ilock(Lock *l)
 			l->sr = x;
 			l->pc = pc;
 			l->pid = pid;
-			l->pri = 0;
 			return;
 		}
 	}
@@ -107,13 +87,7 @@ canlock(Lock *l)
 		return 0;
 
 	l->pc = getcallerpc(l);
-	if(up){
-		l->pid = up->pid;
-		l->pri = up->priority;
-	} else {
-		l->pid = 0;
-		l->pri = 0;
-	}
+	l->pid = up ? up->pid : 0;
 	return 1;
 }
 
@@ -122,7 +96,6 @@ unlock(Lock *l)
 {
 	l->key = 0;
 	l->pc = 0;
-	l->pri = 0;
 }
 
 void
@@ -133,6 +106,5 @@ iunlock(Lock *l)
 	sr = l->sr;
 	l->key = 0;
 	l->pc = 0;
-	l->pri = 0;
 	splx(sr);
 }
diff --git a/power/dat.h b/power/dat.h
index b70b42b8a673b8a71e9179beeebe5eb086c04905..1f00ead903a08150e38a5d8012e9b49a58708cc5 100644
--- a/power/dat.h
+++ b/power/dat.h
@@ -26,7 +26,6 @@ struct Lock
 	ulong	pc;
 	ulong	sr;
 	ulong	pid;
-	int	pri;
 };
 
 struct Label