[uml-devel] ubd=mmap problem

[uml-devel] ubd=mmap problem

[Sven 'Darkman' Michels]

Hi there,

i started uml with udb=mmap, the box runs fine but today i
noticed that the box was terminated after a nightly cron
run inside the uml. While trying to figure out what the
problem was, i noticed that the uml can't reboot anymore
cause it hangs in an endless loop when unmounting the devices.
all i saw was:
map : /proc/mm map failed, err = 9
map : /proc/mm map failed, err = 9
map : /proc/mm map failed, err = 9
map : /proc/mm map failed, err = 9
map : /proc/mm map failed, err = 9
map : /proc/mm map failed, err = 9

this was with 2.4.23 and latest uml 2.4.22 patch. So i thought
its an problem with the patches and builded a fres 2.4.23 with
the latest -1 patch. But the problem is still there. When i
remove the udb=mmap from my startup line, uml works and reboots
like expected. Anyone had that too or can tell me what the
Problem is? ;) The host is running 2.4.22 with skas patch.

Regards,
Sven



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Re: [uml-devel] ubd=mmap problem

[BlaisorBlade]

Alle 14:03, giovedì 25 dicembre 2003, Sven 'Darkman' Michels ha scritto:
> Hi there,
>
> i started uml with udb=mmap, the box runs fine but today i
> noticed that the box was terminated after a nightly cron
> run inside the uml.
This first problem is a known one. Did you mount the host root with hostfs 
inside Uml? If yes, check /var/log/messages and you should see an Oops from 
the host kernel. If that happens, apply on the host the patch in this thread 
on 10 Dec 2003:

[uml-devel] [PATCH] fix for: Host panic when UML reads host /dev/shm

For the second I can't help you, probably it is a still unknown bug, someone 
else will help you or post a fix.

-- 
cat <<EOSIGN
Paolo Giarrusso, aka Blaisorblade
Linux Kernel 2.4.21/2.6.0-test on an i686; Linux registered user n. 292729
EOSIGN



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Re: [uml-devel] ubd=mmap problem

[Jeff Chua]

On Fri, 26 Dec 2003, BlaisorBlade wrote:

> This first problem is a known one. Did you mount the host root with hostfs
> inside Uml? If yes, check /var/log/messages and you should see an Oops from
> the host kernel. If that happens, apply on the host the patch in this thread
> on 10 Dec 2003:
>
> [uml-devel] [PATCH] fix for: Host panic when UML reads host /dev/shm

Can you please repost this patch?

Thanks,
Jeff



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[uml-devel] Re: [uml-user] ubd=mmap problem

[Jeff Dike]

sven@darkman.de said:
> i noticed that the uml can't reboot anymore cause it hangs in an
> endless loop when unmounting the devices. all i saw was: 
> map : /proc/mm map failed, err = 9 

I take it this is reproducable?  ubd-mmap has been stable here, so there's
something about what you're doing that's sending it off the deep end.

The best way I can think to debug it is to stick printks where /proc/mm and
ubd devices get opened and closed showing what file descriptor is involved.
Apparently, the ubd driver is closing a file descriptor that UML thinks is 
a /proc/mm descriptor.

So, could you add printks for the following values in the following places -
    fd in arch/um/kernel/skas/process.c:get_mm() after the os_open_file
    mm->context.skas.mm_fd in arch/um/kernel/skas/mmu.c:destroy_context_skas()
    
    fd in arch/um/drivers/ubd_user.c:open_ubd_file() before the os_lock_file
    dev->fd and dev->cow.fd in arch/um/drivers/ubd_kern.c:ubd_close() before
their respective calls to os_close_file

Make sure that logging is set up so that printks show up in the messages file
or on the console so that you don't lose any of it.

What I think you're looking for is ubd_close closing a /proc/mm descriptor.
This would explain things going to hell when devices are being unmounted.

I'm a little suspicious of the fact that ubd_close doesn't set the descriptors
to -1 after closing them, but I don't see a bug there offhand.

				Jeff


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