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Re: panic on shutdown



On Thu, Sep 11, 2008 at 09:48:42PM +0930, Brett Lymn wrote:
> On Wed, Sep 10, 2008 at 09:58:22PM +0300, Stathis Kamperis wrote:
> > > > Using kernels from Sunday and today, I'm seeing a panic involving
> > >  >  kmem_poison_check on shutdown.  This is using amd64 on a Thinkpad T61.
> > >  >  Is anyone else seeing this?  Sorry I don't have more details; I was
> > >  >  concentrating more on testing if a particular PR had been resolved.
> > >  >
> > >  >
> > >  >                 --Steve Bellovin, http://www.cs.columbia.edu/~smb
> > >  >
> > >
> > >
> > > I am seeing this also. It is triggered when unmounting mfs but I din't
> > >  pay close attention to it either.
> > >
> > >  My system is NetBSD 4.99.72/i386, UP.
> > >
> 
> Yes, there does appear to be a problem with MFS - I have seen two
> behaviours when shutting down the machine:
> 
> 1) Machine panics with a bad memory reference in VFS_START+0x25 -
> which looks to be the unlock of the mount point

I tracked this down to vfs_destroy() being called one too many times.
The struct mount gets freed and thus when VFS_START tries using it again
the pointer is invalid.

I haven't tried very hard to debug it further, this is a case of
whatever printf you add will make the issue go away, but the point is
that reference counting goes wrong.

> 2) Machine just wedges - breaking to ddb just has it waiting on a lock

I've never seen that one.

-- 
Quentin Garnier - cube%cubidou.net@localhost - cube%NetBSD.org@localhost
"See the look on my face from staying too long in one place
[...] every time the morning breaks I know I'm closer to falling"
KT Tunstall, Saving My Face, Drastic Fantastic, 2007.

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