[uml-devel] unable to unmount tmpfs problem lives on

[uml-devel] unable to unmount tmpfs problem lives on

[Christopher S. Aker]

I'm still seeing the "unable to unmount tmpfs" problem like we had before the
fix-kill patch.  All my UMLs have the fix-kill fixes, and yet under some
circumstances (yet unknown), the host kernel refuses to unmount the tmpfs mount that
a UML had used for its VM file.

It's happening under a number of kernels:

2.6.9
2.6.9-ck3
2.6.10-rc2-bk7

lsof shows nothing, but umount still complains that the mountpoint is in-use.

-Chris



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Re: [uml-devel] unable to unmount tmpfs problem lives on

[Christopher S. Aker]

> Well, this is yet undiagnosed, but definitely it's not a UML bug... you should
> certainly run a 2.6.8.1 based kernel...

That is unfortunate.

> There is some kind of security bug fixed in 2.6.9, but it was a littler one
> probably (an overflow when handling file position...).
>
> Do you remember when UML crashed and left the unkillable 'D' thread? That's a
> local DoS bug, and this one you're speaking about is a worse one... I and
> Bodo have complained about this one (not on LKML) and didn't get any answer
> yet...

I could try and get a response from LKML, but you would probably present the problem
better...

-Chris



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Re: [uml-devel] unable to unmount tmpfs problem lives on

[Paolo Giarrusso]

On Friday 17 December 2004 01:24, Christopher S. Aker wrote:
> > Well, this is yet undiagnosed, but definitely it's not a UML bug... you
> > should certainly run a 2.6.8.1 based kernel...
>
> That is unfortunate.
>
> > There is some kind of security bug fixed in 2.6.9, but it was a littler
> > one probably (an overflow when handling file position...).
> >
> > Do you remember when UML crashed and left the unkillable 'D' thread?
> > That's a local DoS bug, and this one you're speaking about is a worse
> > one... I and Bodo have complained about this one (not on LKML) and didn't
> > get any answer yet...
>
> I could try and get a response from LKML, but you would probably present
> the problem better...
I've been away from the net one week, and I've posted the message before it. 
Now, I *do* want to wait before posting to LKML... I'll maybe complain 
louder. I'll post to LKML as a last resort, if they show not enough care of 
the problem, to urge them to fix it.

-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade


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Re: [uml-devel] unable to unmount tmpfs problem lives on

[Christopher S. Aker]

A little more info...

My method for causing the problem every time (example works under 2.6.9-ck3 and
2.6.10-rc2-bk7)

# mount tmpfs tmp/ -t tmpfs
# TMPDIR=./tmp/ /kernels/non-fix-kill-patched-kernel rootfs=debian.fs
# uml_mconsole .uml/xxx/mconsole cad
# kill -KILL <pid1> <pid2>
# umount tmp/
umount: /root/tmp: device is busy

(cad is set to shutdown in the UML's inittab.  After sending CAD, it hangs, which
requires kill)

Under 2.6.10-rc3-bk10 this works fine --the tmpfs mount is unmounted without
problems.  Perhaps it's fixed in recent patches. :)

-Chris



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