Re: [9fans] That deadlock, again

[lucio@proxima.alt.za]

> cinap is right, the bug is in the kernel.  we know
> that because it's a lock loop.  that can only happen
> if the kernel screws up.  also, the address is a kernel
> address (starts with 0xf).

Well, here is an acid dump, I'll inspect it in detail, but I'm hoping
someone will beat me to it (not hard at all, I have to confess):

rumble# acid /sys/src/9/pc/9pccpuf
/sys/src/9/pc/9pccpuf:386 plan 9 boot image
/sys/lib/acid/port
/sys/lib/acid/386

# lock 0xf0057d74 loop key 0xdeaddead pc 0xf01e736a held by pc 0xf01e736a proc 2052

acid: src(0xf01e736a)
/sys/src/9/port/qlock.c:29
 24			print("qlock: %#p: nlocks %lud\n", getcallerpc(&q), up->nlocks.ref);
 25
 26		if(q->use.key == 0x55555555)
 27			panic("qlock: q %#p, key 5*\n", q);
 28		lock(&q->use);
>29		rwstats.qlock++;
 30		if(!q->locked) {
 31			q->locked = 1;
 32			unlock(&q->use);
 33			return;
 34		}

# 61:etherread4 pc f01ef8a0 dbgpc        0   Running (Running) ut 2923 st 0 bss 0 qpc f0148c8a nl 0 nd 0 lpc f0100f6e pri 13

acid: src(0xf01ef8a0)
/sys/src/9/port/taslock.c:96
 91		lockstats.glare++;
 92		for(;;){
 93			lockstats.inglare++;
 94			i = 0;
 95			while(l->key){
>96				if(conf.nmach < 2 && up && up->edf && (up->edf->flags & Admitted)){
 97					/*
 98					 * Priority inversion, yield on a uniprocessor; on a
 99					 * multiprocessor, the other processor will unlock
 100					 */
 101					print("inversion %#p pc %#lux proc %lud held by pc %#lux proc %lud\n",
acid: src(0xf0148c8a)
/sys/src/9/ip/tcp.c:2096
 2091		if(waserror()){
 2092			qunlock(s);
 2093			nexterror();
 2094		}
 2095		qlock(s);
>2096		qunlock(tcp);
 2097
 2098		/* fix up window */
 2099		seg.wnd <<= tcb->rcv.scale;
 2100
 2101		/* every input packet in puts off the keep alive time out */
acid: src(0xf0100f6e)
/sys/src/9/pc/cga.c:112
 107				return;
 108		}
 109		else
 110			lock(&cgascreenlock);
 111
>112		while(n-- > 0)
 113			cgascreenputc(*s++);
 114
 115		unlock(&cgascreenlock);
 116	}
 117

# 2052:  exportfs pc f01e7377 dbgpc     94ad    Pwrite (Ready) ut 55 st 270 bss 40000 qpc f0145b62 nl 1 nd 0 lpc f01e2c60 pri 10

acid: src(0xf01e7377)
/sys/src/9/port/qlock.c:30
 25
 26		if(q->use.key == 0x55555555)
 27			panic("qlock: q %#p, key 5*\n", q);
 28		lock(&q->use);
 29		rwstats.qlock++;
>30		if(!q->locked) {
 31			q->locked = 1;
 32			unlock(&q->use);
 33			return;
 34		}
 35		if(up == 0)
acid: src(0xf0145b62)
/sys/src/9/ip/tcp.c:704
 699	tcpgo(Tcppriv *priv, Tcptimer *t)
 700	{
 701		if(t == nil || t->start == 0)
 702			return;
 703
>704		qlock(&priv->tl);
 705		t->count = t->start;
 706		timerstate(priv, t, TcptimerON);
 707		qunlock(&priv->tl);
 708	}
 709
acid: src(0xf01e2c60)
/sys/src/9/port/proc.c:345
 340	queueproc(Schedq *rq, Proc *p)
 341	{
 342		int pri;
 343
 344		pri = rq - runq;
>345		lock(runq);
 346		p->priority = pri;
 347		p->rnext = 0;
 348		if(rq->tail)
 349			rq->tail->rnext = p;
 350		else
acid: