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fix potential double ready in postnote() for rendezvous

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

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

@@ -95,7 +95,7 @@

 			procalloc.free = up;

 			/* proc is free now, make sure unlock() wont touch it */

-			up = procalloc.p = nil;

+			up = procalloc.Lock.p = nil;

 			unlock(&procalloc);

 			sched();

 		}

@@ -418,7 +418,7 @@

 		print("double ready %s %lud pc %p\n", p->text, p->pid, getcallerpc(&p));

 		return;

 	}

-		

+

 	s = splhi();

 	if(edfready(p)){

 		splx(s);

@@ -984,16 +984,16 @@

 		if(p->state == Rendezvous) {

 			Proc *d, **l;

-			p->rendval = ~0;

 			l = &REND(p->rgrp, p->rendtag);

 			for(d = *l; d; d = d->rendhash) {

 				if(d == p) {

 					*l = p->rendhash;

+					p->rendval = ~0;

+					ready(p);

 					break;

 				}

 				l = &d->rendhash;

 			}

-			ready(p);

 		}

 		unlock(p->rgrp);

 		break;

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

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

@@ -811,7 +811,6 @@

 	tag = arg[0];

 	l = &REND(up->rgrp, tag);

-	up->rendval = ~(uintptr)0;

 	lock(up->rgrp);

 	for(p = *l; p; p = p->rendhash) {

@@ -819,11 +818,10 @@

 			*l = p->rendhash;

 			val = p->rendval;

 			p->rendval = arg[1];

-

+			unlock(up->rgrp);

 			while(p->mach != 0)

 				;

 			ready(p);

-			unlock(up->rgrp);

 			return val;

 		}

 		l = &p->rendhash;