svn commit: r240822 - head/sys/geom

[Andrey Chernov]

On Tue, Sep 25, 2012 at 05:37:12PM -0600, Kenneth D. Merry wrote:
> >   Use the topology lock to protect list of providers while withering them.
> >   It is possible that provider is destroyed while we are iterating over the
> >   list.
> 
> This breaks devices going away in CAM.
> 
> When the da(4) driver calls disk_gone(), it is necessarily holding the SIM
> lock, which is a regular MTX_DEF mutex.  The GEOM topology lock is an sx
> lock, and of WITNESS blows up because of that:

I don't know is it related, but in recent -current I got stable panic at 
the very last stage of reboot (after buffers syncing):
reboot after panic: mutex Giant owned at ../../../geom/geom_disk.c:638
using just plain AHCI disks perhaps attached to CAM.

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