Re: [uml-devel] Host panic when UML reads host /dev/shm

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 19:56, giovedì 20 novembre 2003, Frank Dekervel ha scritto:
> Op Thursday 20 November 2003 19:15, schreef BlaisorBlade:
> > I reported that if I leave an UML sleeping, it segfaults(once I saw the
> > killed by SIGSEGV from the shell, the other time nothing, maybe I had
> > detached the job from the shell).
> >
> > Now I've seen that what happens is that the host kernel oopses. I'm
> > posting it here to collect a bit more infos before posting it to the
> > LKML, and to know why only UML is able to trigger it. Since the bug seems
> > related only to /dev/shm, maybe you could have some enlightenment about
> > it and how UML uses shared memory to make this happen.
>
> i saw the same crash.
Only an oops on linux or the same oops? If the second, it's useful news
> i worked around it by not using hostfs ...
So, probably there was a process runned from inside UML triggering the bug.

In fact, I'm seeing now 4:40, the time the oops happens, is when the slackware 
every day runs updatedb.

A little transcript from a UML session:

root [~: slack90: 1 (0)] # mount
/dev/ubda on / type ext3 (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
proc on /proc type proc (rw)
host on /mnt/host type hostfs (rw,/)
root [~: slack90: 1 (0)] # ls /mnt/host/dev/sh
sheep_net  shm        shmiq
root [~: slack90: 1 (0)] # ls /mnt/host/dev/shm
<Pause because of the same host kernel oops.>

The host shell reported Segmentation fault(wrongly), so all the crashes I had 
were due to this. I can even get the processes in D state(even a ls /dev/shm 
suffices).

Thanks, Frank. Your message was very useful and enlightening.

I think hostfs reads files just as any normal process on the host, right? Or 
it does anything special or at least unusual?

Could the unusual thing be the context switching of SKAS?
I'll test if it happens within TT mode. Jeff, this seems easy reproduceable, 
so try it, please.

Bye
-- 
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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