From 2f9960b6a2a96ce115350b9b954cab1915edfd22 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Wed, 22 May 1996 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1996-05-22

---
 pc/ether589.c  |  6 +---
 port/proc.c    |  1 +
 port/taslock.c | 82 ++++++++++++++++++++++++++++++++------------------
 3 files changed, 54 insertions(+), 35 deletions(-)

diff --git a/pc/ether589.c b/pc/ether589.c
index 8a30d22ff61d72644738b1d5b4d4aeec939e50d7..6e2b7127cd002d7ff7b88a31d8cfa47d70eea57f 100644
--- a/pc/ether589.c
+++ b/pc/ether589.c
@@ -46,7 +46,6 @@ static int
 configASIC(Ether *ether, int port, int xcvr)
 {
 	ushort x;
-int r;
 
 	/* set Window 0 configuration registers */
 	COMMAND(port, SelectWindow, 0);
@@ -54,7 +53,6 @@ int r;
 	/* ROM size & base - must be set before we can access ROM */
 	/* transceiver type is 2 for 'figure it out'  */
 	x = ins(port + AddressConfig);
-print("x = %uX\n", x);
 	outs(port + AddressConfig, (x & 0xf0) | xcvr);
 
 	/* IRQ must be 3 on 3C589 */
@@ -70,9 +68,7 @@ print("x = %uX\n", x);
 	x = ins(port+EEPROMdata);
 	outs(port + ProductID, x);
 
-	r = ether509reset(ether);
-	outs(port + ResourceConfig, 0x3f00);
-	return r;
+	return ether509reset(ether);
 }
 
 static int
diff --git a/port/proc.c b/port/proc.c
index 5d92c7dc12e7fc654e0cd943b581d65d7e4a9873..c0b1e1a1095987015a700544cf68a8d058ec4ded 100644
--- a/port/proc.c
+++ b/port/proc.c
@@ -327,6 +327,7 @@ newproc(void)
 	p->wired = 0;
 	p->ureg = 0;
 	p->error[0] = '\0';
+	p->lockpri = 0;
 	memset(p->seg, 0, sizeof p->seg);
 	p->pid = incref(&pidalloc);
 	p->noteid = incref(&noteidalloc);
diff --git a/port/taslock.c b/port/taslock.c
index a8a189af82ba7f52d549e8605b108129c94279cd..789ed0859c3f19860746a8cc5851fa918131dad3 100644
--- a/port/taslock.c
+++ b/port/taslock.c
@@ -13,41 +13,60 @@ lockloop(Lock *l, ulong pc)
 	dumpaproc(up);
 }
 
+#define LOCKLOOP 100000000	/* to detect a lock loop */
+#define SPINLOOP 10000000	/* to keep tas's off the bus */
+
 void
 lock(Lock *l)
 {
-	int pri, i;
-	ulong pc;
+	int i, pri, spins;
+	ulong pc, pid;
 
 	pc = getcallerpc(l);
+	if(up){
+		pid = up->pid;
+		pri = up->priority;
+	} else {
+		pid = 0;
+		pri = 0;
+	}
 
-	if(up == 0) {
-		for(i=0; i<1000000; i++)
-			if(tas(&l->key) == 0){
-				l->pc = pc;
-				l->pri = 0;
-				return;
-			}
-		lockloop(l, pc);
+	/* quick try, it might work */
+	if(tas(&l->key) == 0){
+		l->pc = pc;
+		l->pid = pid;
+		l->pri = pri;
 		return;
 	}
 
-	/* priority interacts with code in ready() in proc.c */
-	pri = up->priority;
+	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();
+				}
+			}
 
-	for(i=0; i<1000000; i++){
-		up->lockpri = l->pri;		/* assume priority of process holding lock */
 		if(tas(&l->key) == 0){
-			l->pri = pri;
-			up->lockpri = 0;	/* back to normal priority */
 			l->pc = pc;
+			l->pid = pid;
+			l->pri = pri;
+			up->lockpri = 0;
 			return;
 		}
-		if(conf.nmach == 1 && up->state == Running && (getstatus()&IE))
-			sched();
 	}
-	lockloop(l, pc);
-	up->lockpri = 0;	/* back to normal priority */
 }
 
 void
@@ -64,6 +83,7 @@ ilock(Lock *l)
 		l->sr = x;
 		l->pc = pc;
 		l->pid = pid;
+		l->pri = 0;
 		return;
 	}
 
@@ -74,6 +94,7 @@ ilock(Lock *l)
 			l->sr = x;
 			l->pc = pc;
 			l->pid = pid;
+			l->pri = 0;
 			return;
 		}
 	}
@@ -82,25 +103,25 @@ ilock(Lock *l)
 int
 canlock(Lock *l)
 {
-	int pri;
-
-	if(up)
-		pri = up->priority;
-	else
-		pri = 0;
-	if(tas(&l->key)) {
-		l->pc = getcallerpc(l);
+	if(tas(&l->key))
 		return 0;
+
+	l->pc = getcallerpc(l);
+	if(up){
+		l->pid = up->pid;
+		l->pri = up->priority;
+	} else {
+		l->pid = 0;
+		l->pri = 0;
 	}
-	l->pri = pri;
 	return 1;
 }
 
 void
 unlock(Lock *l)
 {
-	l->pc = 0;
 	l->key = 0;
+	l->pc = 0;
 	l->pri = 0;
 }
 
@@ -112,5 +133,6 @@ iunlock(Lock *l)
 	sr = l->sr;
 	l->key = 0;
 	l->pc = 0;
+	l->pri = 0;
 	splx(sr);
 }