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Date: Tue, 12 Aug 1997 20:05:39 -0700
From: Julian Elischer <julian@whistle.com>
Organization: Whistle Communications
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To: Michael Smith <msmith@atrad.adelaide.edu.au>
CC: julian@FreeBSD.ORG, hackers@FreeBSD.ORG
Subject: Re: 2.2.2+ crash.. more info
References: <199708130234.MAA11390@genesis.atrad.adelaide.edu.au>
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Michael Smith wrote:
> 
> Julian Elischer stands accused of saying:
> > Michael Smith wrote:
> > >
> > > Julian Elischer stands accused of saying:
> > > >
> > > > We have several hundred Bsd machines here.. we see this one 
> > > > enough for
> > > > me to recognise it..

> > the fact that the process got put on the a sleep queue while it was
> > on the runnable queue. suggests that maybe an interrupt driver
> > ran 'tsleep' while curproc had the value of this process in it..
stupidly I have a big clue right in front of me that I didn't mention..

the process in question has a wait channel of 'swread'
that's in the VM code..
in fact, in:
static int swap_pager_getpages(object, m, count, reqpage)
...
        /*
         * wait for the sync I/O to complete
         */
        s = splbio();
        while ((bp->b_flags & B_DONE) == 0) {
                if (tsleep(bp, PVM, "swread", hz*20)) {
                        printf("swap_pager: indefinite wait buffer:
device: %d,
blkno: %d, size: %d\n",
                                bp->b_dev, bp->b_blkno, bp->b_bcount);
                }       
        }



what I wonder about is: does this ever get run in the context of
another process?  who runs this?
etc.

I think (after discussion with john) that the quick test will be to 
add code to tsleep to check if the process being slept is still on the 
run queue..