From owner-freebsd-current  Sun Jan 13  3:37: 4 2002
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Date: Sun, 13 Jan 2002 22:37:35 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Michael Reifenberger <root@nihil.plaut.de>
Cc: FreeBSD-Current <current@FreeBSD.ORG>
Subject: Re: panic during fdisk'ing a md(4) device
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On Sat, 12 Jan 2002, Michael Reifenberger wrote:

> Hi,
> more input:
> The panic occurs in dsname() while dereferencing devsw(dev)->d_name.
> devsw(dev) gives NULL.

This was fairly clear from the panic message (the low fault address
is almost certainly for a null pointer + offset, and it's fairly clear
how dsname() gets a null pointer).  Sorry I didn't reply earlier and
save you the work debugging this.

> The call to dsname() occurs from dkmodminor() defined in disklabel.h
> I've seen two calls to dsname, only the second one panics.
> Any thoughts?

dkmodminor() is supposed to modify a minor device that already has a
devswitch.  Since dsname() in it panics, the problem is earlier when
the minor device is created without giving it a devswitch.  Minor
devices are supposed to be created in a hierarchial order so that
this doesn't happen.  E.g.,

    ad0                  in disk_create() (only ?)
        ad0s1            now in dsopen()
        ad0s2
            ad0s2a       now in dsopen()
            ...

I suggest adding printfs to make_dev() and makedev() to track the order.
The problem occurs when makedev() is called without a corresponding
make_dev().

Bruce


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