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uml | 1 Feb 2006 04:23

[uml-user] random guest processes segfault


I tried upgrading my UML running 2.4.28-1um to 2.6.15.2-bs1. After bringing
the UML up under the later kernel, I noticed random processes within the UML
would segfault. For instance, I tried SSHing to it over and over and in
about 1 in 5 attempts my shell or something else during the login procedure
would segfault before getting to a prompt.

/lib/tls has been moved to /lib/tls.disabled and I stopped & restarted the
UML after making that change, didn't help.

Nothing distinct was printed to the guest's syslog or kernel log except
"line_write_room: tty0: no room left in buffer", but the occurance of those
messages didn't seem to correlate with the segfaults.

I reverted back to 2.4.28-1um and everything is fine again.

The only other changes I made were switching from devfs to regular device
files in 2.6, and booting the 2.6 kernel with more memory (this 2.4 image I
have has TT enabled and won't start with more than mem=200M).

Any ideas? Any other info I can post?

Thanks

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Blaisorblade | 1 Feb 2006 15:24
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Re: [uml-user] Network configuration

On Tuesday 31 January 2006 21:04, Adam Atlas wrote:
> On 31 Jan 2006, at 12.57, Blaisorblade wrote:
> > If it's on the same subnet as the host one, simply remove that IP
> > from the
> > host and give it to the guest following the normal configuration
> > steps...
> >
> > If not, it can be accomplished, just I'm too lazy and busy to write
> > it here
> > for now :-)
>
> It is indeed on the same subnet.
>
> Where do I start? Which normal configuration steps are you referring
> to? I haven't done this before...

A few links for guides:

http://user-mode-linux.sourceforge.net/ (search network)

http://uml.harlowhill.com/

http://www.user-mode-linux.org/~blaisorblade (see the Links page).

--

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
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Blaisorblade | 1 Feb 2006 15:28
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Re: [uml-user] random guest processes segfault

On Wednesday 01 February 2006 04:23, uml <at> s.rhythm.cx wrote:
> I tried upgrading my UML running 2.4.28-1um to 2.6.15.2-bs1. After bringing
> the UML up under the later kernel, I noticed random processes within the
> UML would segfault. For instance, I tried SSHing to it over and over and in
> about 1 in 5 attempts my shell or something else during the login procedure
> would segfault before getting to a prompt.

> /lib/tls has been moved to /lib/tls.disabled and I stopped & restarted the
> UML after making that change, didn't help.

> Nothing distinct was printed to the guest's syslog or kernel log except
> "line_write_room: tty0: no room left in buffer"

That's indeed harmless... but didn't the ssh log contain anything?

> , but the occurance of those 
> messages didn't seem to correlate with the segfaults.

> I reverted back to 2.4.28-1um and everything is fine again.

> The only other changes I made were switching from devfs to regular device
> files in 2.6, and booting the 2.6 kernel with more memory (this 2.4 image I
> have has TT enabled and won't start with more than mem=200M).

> Any ideas? Any other info I can post?
Never seen such a report... guess that knowing which guest distro, which mode 
(SKAS0 or TT or SKAS3), the command line and the kernel config (can be 
obtained with the --showconfig switch).

> Thanks
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uml | 1 Feb 2006 15:58

Re: [uml-user] random guest processes segfault


Resending, forgot to CC the list. Please excuse my dupe Blaisorblade.

On Wed, Feb 01, 2006 at 03:28:21PM +0100, Blaisorblade wrote:
> That's indeed harmless... but didn't the ssh log contain anything?

Nope. I was watching all syslog messages (all facilities, level debug and
higher) and no errors were reported.

I did catch one such segfault while logging in with strace. It was
/bin/login which segfaulted, at least that time.

> Never seen such a report... guess that knowing which guest distro, which mode 
> (SKAS0 or TT or SKAS3), the command line and the kernel config (can be 
> obtained with the --showconfig switch).

Guest distro: Debian Sarge 

Mode: SKAS3 

Kernel command line: ubd0=root_fs ubd1=u_fs ubd2=swap ubd3=var_fs mem=384M
eth0=tuntap,tap0 root=/dev/ubd0

Kernel config follows:

#
# Automatically generated make config: don't edit
# Linux kernel version: 2.6.15.2-bs1
# Tue Jan 31 21:08:09 2006
#
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Blaisorblade | 1 Feb 2006 15:23
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Fwd: Re: [uml-user] Static Multicast Routing on UML...

I'm forwarding the email to the ML since it's intended for that (and I've no 
time to answer right now).

Btw, I think the problem is more likely to lie on port = 0 than on INADDR_ANY 
(you'd at least need to be root to use a port < 1024, and I think port 0 is 
invalid).

----------  Forwarded Message  ----------

Subject: Re: [uml-user] Static Multicast Routing on UML...
Date: Wednesday 01 February 2006 00:09
From: frank evans <princedwardisland <at> gmail.com>
To: Blaisorblade <blaisorblade <at> yahoo.it>

HI UML'ers...

OK, I have another issue:  I have a UML (linux-2.4.28 with Debian FS)
running, with eth0 hooked to the uml_switch.  I have a little program I run
on the UML, that wants to open up a UDP socket with an address of INADDR_ANY,
and a Port = 0.  When the program does a connect( Sock, (struct sockaddr
*)&SockAdr, sizeof( SockAdr ) call which returns an error code of ERRO: UDP
socket connect; Errno(22): Invalid argument.  I am wondering if there is
something that does not like INADDR_ANY?

Got any ideas?

Thanks,
Ben Evans

On 1/27/06, frank evans <princedwardisland <at> gmail.com> wrote:
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Allen Chan | 1 Feb 2006 21:28
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Re: [uml-user] random guest processes segfault

On Tuesday 31 January 2006 22:23, uml <at> s.rhythm.cx wrote:
> I tried upgrading my UML running 2.4.28-1um to 2.6.15.2-bs1. After
> bringing the UML up under the later kernel, I noticed random
> processes within the UML would segfault. For instance, I tried
> SSHing to it over and over and in about 1 in 5 attempts my shell or
> something else during the login procedure would segfault before
> getting to a prompt.

I've had similar problems in every UML guest kernel starting with 
2.6.11.  The initial ssh login would segfault every now and then, but 
the UML appears to run fine otherwise.  The same setup would work 
fine in a 2.4.* guest kernel and in 2.6.* guest kernels up to 2.6.10.

After a little experimentation, it appears that the problem only 
occurs in a tcsh shell and the segfault occurs on command lines 
containing backquotes, and even then, the segfault only occurs 
roughly 10% of the time.  The problem can be reproduced by repeatedly 
executing the following command inside the UML guest:
	tcsh -c 'echo `hostname`'

Unfortunately, I have not found a solution other than to avoid tcsh 
and/or backquoted commands from inside tcsh scripts.

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uml | 1 Feb 2006 22:10

Re: [uml-user] random guest processes segfault

On Wed, Feb 01, 2006 at 03:28:06PM -0500, Allen Chan wrote:
> On Tuesday 31 January 2006 22:23, uml <at> s.rhythm.cx wrote:
> > I tried upgrading my UML running 2.4.28-1um to 2.6.15.2-bs1. After
> > bringing the UML up under the later kernel, I noticed random
> > processes within the UML would segfault. For instance, I tried
> > SSHing to it over and over and in about 1 in 5 attempts my shell or
> > something else during the login procedure would segfault before
> > getting to a prompt.
> 
> I've had similar problems in every UML guest kernel starting with 
> 2.6.11.  The initial ssh login would segfault every now and then, but 
> the UML appears to run fine otherwise.  The same setup would work 
> fine in a 2.4.* guest kernel and in 2.6.* guest kernels up to 2.6.10.
> 
> After a little experimentation, it appears that the problem only 
> occurs in a tcsh shell and the segfault occurs on command lines 
> containing backquotes, and even then, the segfault only occurs 
> roughly 10% of the time.  The problem can be reproduced by repeatedly 
> executing the following command inside the UML guest:
> 	tcsh -c 'echo `hostname`'

Ah, yes, mine is doing the exact same thing. 

I made it core dump, but the core it left behind is corrupt or something.
gdb says it segfaulted while doing read() in libc, but there are thousands
of bogus frames on the stack, so who knows...

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Jeff Dike | 2 Feb 2006 17:23

Re: [uml-user] random guest processes segfault

On Wed, Feb 01, 2006 at 03:28:06PM -0500, Allen Chan wrote:
The problem can be reproduced by repeatedly 
> executing the following command inside the UML guest:
> 	tcsh -c 'echo `hostname`'

Nice test case!  This appears to be a skas0 bug - the skas0 segfault handler
is segfaulting for some reason, and this is causing the process to segfault.

				Jeff

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Allen Chan | 2 Feb 2006 18:01
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Re: [uml-user] random guest processes segfault

On Thursday 02 February 2006 11:23, Jeff Dike wrote:
> On Wed, Feb 01, 2006 at 03:28:06PM -0500, Allen Chan wrote:
>> The problem can be reproduced by repeatedly
> > executing the following command inside the UML guest:
> > 	tcsh -c 'echo `hostname`'
>
> Nice test case!  This appears to be a skas0 bug - the skas0
> segfault handler is segfaulting for some reason, and this is
> causing the process to segfault.

This issue may not be limited to skas0, as I'm encountering these 
symptoms while using skas3 patched hosts, both on my own machines and 
on a UML guest hosted at linode.com.

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uml | 2 Feb 2006 19:17

Re: [uml-user] random guest processes segfault

On Thu, Feb 02, 2006 at 12:01:26PM -0500, Allen Chan wrote:
> This issue may not be limited to skas0, as I'm encountering these 
> symptoms while using skas3 patched hosts, both on my own machines and 
> on a UML guest hosted at linode.com.

I'm also seeing this on skas3.

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Gmane