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From: Lucio De Re <lucio@proxima.alt.za>
To: 9fans@9fans.net
Subject: Re: [9fans] That deadlock, again
Date: Thu, 18 Nov 2010 07:50:49 +0200	[thread overview]
Message-ID: <215c4028dc0c6d0cdcda7fd23830bc70@proxima.alt.za> (raw)

> one could move:
>
> 	up->qpc = getcallerpc(&q);
>
>  from qlock() before the lock(&q->use); so we can see from where that
> qlock gets called that hangs the exportfs call, or add another magic
> debug pointer (qpctry) to the proc stucture and print it in dumpaproc().


Cinap, I tried your debugging code and got an odd panic at boot time.
Consistently:

	panic: kernel fault: no user process pc=0xf01e739e addr=0x000009e8

Having a look with acid, this seems to be caused by an attempt at
setting the debug PC (your "up->qpctry") at a time when "up" has no
value yet.

Strangely, later in the qlock() code "up" is checked and a panic
issued if zero.  I'm missing something here: it is possible to execute
this code

/sys/src/9/port/qlock.c:29,37 (more or less)
	lock(&q->use);
	rwstats.qlock++;
	if(!q->locked) {
		q->locked = 1;
		unlock(&q->use);
		return;
	}

which is immediately followed by

	if(up == 0)
		panic("qlock");

If "up" is nil, but it looks like a bit of a one-way operation.

Anyway, I have moved the assignment to "qpctry" to after "up" is
tested.  Let's see what happens.  I'll have to get back to you once
the system is back up.

++L




             reply	other threads:[~2010-11-18  5:50 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-11-18  5:50 Lucio De Re [this message]
2010-11-18  5:53 ` erik quanstrom
2010-11-18  8:11   ` Lucio De Re
2010-11-18  8:35     ` cinap_lenrek
2010-11-18  9:20     ` cinap_lenrek
2010-11-18 10:48       ` Lucio De Re
2010-11-18 15:10         ` erik quanstrom
2010-11-18 16:46           ` erik quanstrom
2010-11-18 18:01             ` Lucio De Re
2010-11-18 18:29               ` C H Forsyth
2010-11-18 18:23                 ` Lucio De Re
2010-11-18 18:33                 ` Lucio De Re
2010-11-18 18:43               ` erik quanstrom
2010-11-18 18:54                 ` erik quanstrom
2010-11-18 19:01                 ` Lucio De Re
2010-11-18 19:27                   ` Lucio De Re
2010-11-18 18:03           ` Lucio De Re
2010-11-18  5:57 ` Lucio De Re
  -- strict thread matches above, loose matches on Subject: below --
2010-11-16  4:21 lucio
2010-11-16  4:40 ` erik quanstrom
2010-11-16  5:03   ` lucio
2010-11-16  5:11     ` cinap_lenrek
2010-11-16  5:18       ` lucio
2010-11-16  5:28         ` cinap_lenrek
2010-11-16  6:47           ` Lucio De Re
2010-11-16 13:53     ` erik quanstrom
2010-11-16 18:03       ` lucio
2010-11-17  4:08         ` Lucio De Re
2010-11-17  4:18           ` erik quanstrom
2010-11-17  4:37             ` Lucio De Re
2010-11-17  4:43               ` erik quanstrom
2010-11-17  5:22             ` cinap_lenrek
2010-11-17  6:45               ` Lucio De Re
2010-11-17  7:03                 ` Lucio De Re
2010-11-17  7:09                   ` erik quanstrom
2010-11-17  5:33             ` cinap_lenrek
2010-11-17  6:48               ` Lucio De Re
2010-11-17  7:03                 ` erik quanstrom
2010-11-17 14:40           ` Russ Cox

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