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fix devproc and killbig segment race

we have to acquire p->seglock before we lock the individual
segments of the process and lock them. if we dont then pexit()
might free the segments before we can lock them causing the
"qunlock called with qlock not held, from ..." prints.

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

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

@@ -863,7 +863,13 @@

 			l = TK2MS(l);

 			readnum(0, statbuf+j+NUMSIZE*i, NUMSIZE, l, NUMSIZE);

 		}

+

 		l = 0;

+		eqlock(&p->seglock);

+		if(waserror()){

+			qunlock(&p->seglock);

+			nexterror();

+		}

 		for(i=0; i<NSEG; i++){

 			if(s = p->seg[i]){

 				eqlock(&s->lk);

@@ -871,6 +877,9 @@

 				qunlock(&s->lk);

 			}

 		}

+		poperror();

+		qunlock(&p->seglock);

+

 		readnum(0, statbuf+j+NUMSIZE*6, NUMSIZE, l*BY2PG/1024, NUMSIZE);

 		readnum(0, statbuf+j+NUMSIZE*7, NUMSIZE, p->basepri, NUMSIZE);

 		readnum(0, statbuf+j+NUMSIZE*8, NUMSIZE, p->priority, NUMSIZE);

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

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

@@ -1494,7 +1494,7 @@

 	kp = 0;

 	ep = procalloc.arena+conf.nproc;

 	for(p = procalloc.arena; p < ep; p++) {

-		if(p->state == Dead || p->kp)

+		if(p->state == Dead || p->kp || !canqlock(&p->seglock))

 			continue;

 		l = 0;

 		for(i=1; i<NSEG; i++) {

@@ -1504,12 +1504,13 @@

 			l += (ulong)mcountseg(s);

 			qunlock(&s->lk);

 		}

+		qunlock(&p->seglock);

 		if(l > max && ((p->procmode&0222) || strcmp(eve, p->user)!=0)) {

 			kp = p;

 			max = l;

 		}

 	}

-	if(kp == 0)

+	if(kp == 0 || !canqlock(&kp->seglock))

 		return;

 	print("%lud: %s killed: %s\n", kp->pid, kp->text, why);

 	for(p = procalloc.arena; p < ep; p++) {

@@ -1526,6 +1527,7 @@

 			qunlock(&s->lk);

 		}

 	}

+	qunlock(&kp->seglock);

 }

 /*

-- 

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