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kernel: add pc field in QLock for debugging

Maintain a QLock.pc and RWLock.wpc field which is
the callerpc() of the last owner of the qlock/wlock.

The previous patch that set QLock.use.pc was
kind of nonsensical as it will get overridden
by the next attempt to acquire the qlock.

--- a/sys/src/9/port/portdat.h

+++ b/sys/src/9/port/portdat.h

@@ -78,6 +78,7 @@

 	Lock	use;		/* to access Qlock structure */

 	Proc	*head;		/* next process waiting for object */

 	Proc	*tail;		/* last process waiting for object */

+	uintptr	pc;		/* pc of owner */

 	int	locked;		/* flag */

 };

@@ -93,9 +94,8 @@

 	Proc	*head;		/* list of waiting processes */

 	Proc	*tail;

 	uintptr	wpc;		/* pc of writer */

-	Proc	*wproc;		/* writing proc */

-	int	readers;	/* number of readers */

 	int	writer;		/* number of writers */

+	int	readers;	/* number of readers */

 };

 struct Alarms

--- a/sys/src/9/port/qlock.c

+++ b/sys/src/9/port/qlock.c

@@ -19,19 +19,23 @@

 eqlock(QLock *q)

 {

 	Proc *p;

+	uintptr pc;

+	pc = getcallerpc(&q);

+

 	if(m->ilockdepth != 0)

-		print("eqlock: %#p: ilockdepth %d\n", getcallerpc(&q), m->ilockdepth);

+		print("eqlock: %#p: ilockdepth %d\n", pc, m->ilockdepth);

 	if(up != nil && up->nlocks)

-		print("eqlock: %#p: nlocks %d\n", getcallerpc(&q), up->nlocks);

+		print("eqlock: %#p: nlocks %d\n", pc, up->nlocks);

 	if(up != nil && up->eql != nil)

-		print("eqlock: %#p: eql %p\n", getcallerpc(&q), up->eql);

+		print("eqlock: %#p: eql %p\n", pc, up->eql);

 	if(q->use.key == 0x55555555)

-		panic("eqlock: q %#p, key 5*", q);

+		panic("eqlock: %#p: q %#p, key 5*", pc, q);

 	lock(&q->use);

 	rwstats.qlock++;

 	if(!q->locked) {

+		q->pc = pc;

 		q->locked = 1;

 		unlock(&q->use);

 		return;

@@ -52,7 +56,7 @@

 	q->tail = up;

 	up->eql = q;

 	up->qnext = nil;

-	up->qpc = getcallerpc(&q);

+	up->qpc = pc;

 	up->state = Queueing;

 	unlock(&q->use);

 	sched();

@@ -67,19 +71,22 @@

 qlock(QLock *q)

 {

 	Proc *p;

+	uintptr pc;

+	pc = getcallerpc(&q);

+

 	if(m->ilockdepth != 0)

-		print("qlock: %#p: ilockdepth %d\n", getcallerpc(&q), m->ilockdepth);

+		print("qlock: %#p: ilockdepth %d\n", pc, m->ilockdepth);

 	if(up != nil && up->nlocks)

-		print("qlock: %#p: nlocks %d\n", getcallerpc(&q), up->nlocks);

+		print("qlock: %#p: nlocks %d\n", pc, up->nlocks);

 	if(up != nil && up->eql != nil)

-		print("qlock: %#p: eql %p\n", getcallerpc(&q), up->eql);

+		print("qlock: %#p: eql %p\n", pc, up->eql);

 	if(q->use.key == 0x55555555)

-		panic("qlock: q %#p, key 5*", q);

+		panic("qlock: %#p: q %#p, key 5*", pc, q);

 	lock(&q->use);

 	rwstats.qlock++;

 	if(!q->locked) {

-		q->use.pc = getcallerpc(&q);

+		q->pc = pc;

 		q->locked = 1;

 		unlock(&q->use);

 		return;

@@ -95,8 +102,8 @@

 	q->tail = up;

 	up->eql = nil;

 	up->qnext = nil;

+	up->qpc = pc;

 	up->state = Queueing;

-	up->qpc = getcallerpc(&q);

 	unlock(&q->use);

 	sched();

 }

@@ -111,6 +118,7 @@

 		return 0;

 	}

 	q->locked = 1;

+	q->pc = getcallerpc(&q);

 	unlock(&q->use);

 	return 1;

 }

@@ -126,6 +134,7 @@

 			getcallerpc(&q));

 	p = q->head;

 	if(p != nil){

+		q->pc = p->qpc;

 		q->head = p->qnext;

 		if(q->head == nil)

 			q->tail = nil;

@@ -184,6 +193,7 @@

 	q->head = p->qnext;

 	if(q->head == nil)

 		q->tail = nil;

+	q->wpc = p->qpc;

 	q->writer = 1;

 	unlock(&q->use);

 	ready(p);

@@ -193,13 +203,15 @@

 wlock(RWlock *q)

 {

 	Proc *p;

+	uintptr pc;

+	pc = getcallerpc(&q);

+

 	lock(&q->use);

 	rwstats.wlock++;

 	if(q->readers == 0 && q->writer == 0){

 		/* noone waiting, go for it */

-		q->wpc = getcallerpc(&q);

-		q->wproc = up;

+		q->wpc = pc;

 		q->writer = 1;

 		unlock(&q->use);

 		return;

@@ -216,6 +228,7 @@

 		p->qnext = up;

 	q->tail = up;

 	up->qnext = nil;

+	up->qpc = pc;

 	up->state = QueueingW;

 	unlock(&q->use);

 	sched();

@@ -235,6 +248,7 @@

 	}

 	if(p->state == QueueingW){

 		/* start waiting writer */

+		q->wpc = p->qpc;

 		q->head = p->qnext;

 		if(q->head == nil)

 			q->tail = nil;