Re: [uml-devel] [uml-user] Hanging using 'iptables -L' in UML vm booted with con0=pts

Re: [uml-devel] [uml-user] Hanging using 'iptables -L' in UML vm booted with con0=pts

[Jeff Dike]

On Wed, Sep 05, 2007 at 09:00:51AM +1000, Richard Andrews wrote:
> There is an outstanding kernel + mod_utils bug I am tracking via RedHat that
> exhibits similar behaviour - lockup with 100% CPU in modprobe.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=212922

This one seems not to have anything to do with UML, while the bug that
we're talking about here seems to, as modprobe sometimes works and
sometimes doesn't.

				Jeff

-- 
Work email - jdike at linux dot intel dot com

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Re: [uml-devel] [uml-user] Hanging using 'iptables -L' in UML vm booted with con0=pts

[Blaisorblade]

[-- Attachment #1.1: Type: text/plain, Size: 934 bytes --]

On lunedì 10 settembre 2007, Jeff Dike wrote:
> On Wed, Sep 05, 2007 at 09:00:51AM +1000, Richard Andrews wrote:
> > There is an outstanding kernel + mod_utils bug I am tracking via RedHat
> > that exhibits similar behaviour - lockup with 100% CPU in modprobe.
> >
> > https://bugzilla.redhat.com/show_bug.cgi?id=212922
>
> This one seems not to have anything to do with UML, while the bug that
> we're talking about here seems to, as modprobe sometimes works and
> sometimes doesn't.

My memory remembers that vmalloc() is used both by iptables and by module 
support, and that I've learnt this while we debugged some very old vmalloc 
bug (I may be talking of 2.4.20). I've not had the time to look at that 
report, but does what I say make sense to you?
-- 
"Doh!" (cit.), I've made another mistake!
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade

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Re: [uml-devel] [uml-user] Hanging using 'iptables -L' in UML vm booted with con0=pts

[Jeff Dike]

On Wed, Sep 12, 2007 at 11:52:32PM +0200, Fermín Galán Márquez wrote:
> This is the trace (as you can see I're repeated the experiment twice, 
> the result is basically the same), hoping it could be useful to diagnose 
> the problem and fix eventual bugs in the UML kernel. See below regarding 
> the test procedure.
> 
> (gdb) bt
> #0  0xb7f9d7f2 in ?? () from /lib/ld-linux.so.2
> #1  0xb7f19ab0 in tcsetattr () from /lib/i686/cmov/libc.so.6
> #2  0x080610d5 in generic_console_write (fd=7,
>     buf=0x828fc13 "ip_tables: (C) 2000-2006 Netfilter Core Team\n", n=45)
>     at arch/um/drivers/chan_user.c:37
> #3  0x0806096e in console_write_chan (chans=0x82756f0,
>     buf=0x828fc13 "ip_tables: (C) 2000-2006 Netfilter Core Team\n", len=45)
>     at arch/um/drivers/chan_kern.c:352

Are you capturing UML output with a script or something?  This is the
signature of the script not reading from the pty, so everything just
backs up, waiting for the pty to clear up.

				Jeff

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Re: [uml-devel] [uml-user] Hanging using 'iptables -L' in UML vm booted with con0=pts

[Fermín Galán Márquez]

Dear Jeff,

Jeff Dike wrote:
> On Wed, Sep 12, 2007 at 11:52:32PM +0200, Fermín Galán Márquez wrote:
>> This is the trace (as you can see I're repeated the experiment twice, 
>> the result is basically the same), hoping it could be useful to diagnose 
>> the problem and fix eventual bugs in the UML kernel. See below regarding 
>> the test procedure.
>>
>> (gdb) bt
>> #0  0xb7f9d7f2 in ?? () from /lib/ld-linux.so.2
>> #1  0xb7f19ab0 in tcsetattr () from /lib/i686/cmov/libc.so.6
>> #2  0x080610d5 in generic_console_write (fd=7,
>>     buf=0x828fc13 "ip_tables: (C) 2000-2006 Netfilter Core Team\n", n=45)
>>     at arch/um/drivers/chan_user.c:37
>> #3  0x0806096e in console_write_chan (chans=0x82756f0,
>>     buf=0x828fc13 "ip_tables: (C) 2000-2006 Netfilter Core Team\n", len=45)
>>     at arch/um/drivers/chan_kern.c:352
> 
> Are you capturing UML output with a script or something?  This is the
> signature of the script not reading from the pty, so everything just
> backs up, waiting for the pty to clear up.

AFAIK, no script is capturing (I understand you refers to the output of 
the UML linux executable) and, as a matter of fact, I'm getting some 
output when execute ./linux. To be precise, this is the exact command 
(and the output) I get:

cibeles:/tmp# ./linux ubd0=/tmp/root_fs_debug con=null con0=pts 
uml_dir=/tmp umid=run
Core dump limits :
         soft - 0
         hard - NONE
Checking that ptrace can change system call numbers...OK
Checking syscall emulation patch for ptrace...OK
Checking advanced syscall emulation patch for ptrace...OK
Checking for tmpfs mount on /dev/shm...OK
Checking PROT_EXEC mmap in /dev/shm/...OK
Checking for the skas3 patch in the host:
   - /proc/mm...not found: No such file or directory
   - PTRACE_FAULTINFO...not found
   - PTRACE_LDT...not found
UML running in SKAS0 mode
[no more output, no new prompt]

Then, in a second terminal in the host, I get the pts device and open a 
screen in the vm:

cibeles:/tmp# uml_mconsole run/mconsole config con0
Warning: couldn't stat file: /root/.uml/run/mconsole/mconsole - No such 
file or directory
Warning: couldn't stat file: /tmp/uml/run/mconsole/mconsole - No such 
file or directory
OK pts:/dev/pts/1
cibeles:/tmp# screen /dev/pts/1
[the terminal "goes into" the vm. I use it to cause the fail, as seen below]
Debian GNU/Linux lenny/sid vm tty0

vm login: root
Password:
Last login: Wed Sep 12 23:32:36 2007 on tty0
Linux vm 2.6.22.4-xt-2m #1 Wed Sep 12 20:24:20 CEST 2007 i686

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
vm:~# iptables -L
[no output, linux process reach 100% CPU usage in the host]

In a third host terminal I run gdb:

cibeles:/tmp# cat run/pid
6627
cibeles:/tmp# gdb ./linux 6627

GNU gdb 6.4.90-debian
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain 
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...Using host libthread_db 
library "/lib/i686/cmov/libthread_db.so.1".

Attaching to program: /tmp/linux, process 6627
Reading symbols from /lib/i686/cmov/libutil.so.1...done.
Loaded symbols for /lib/i686/cmov/libutil.so.1
Reading symbols from /lib/i686/cmov/libc.so.6...done.
Loaded symbols for /lib/i686/cmov/libc.so.6
Reading symbols from /lib/ld-linux.so.2...done.
Loaded symbols for /lib/ld-linux.so.2
0xb7f947f2 in ?? () from /lib/ld-linux.so.2
(gdb) bt
[showing the trace I've already sent in the other mail]

Maybe there are "other outputs" apart of the output that the ./linux 
produces which could be causing the problem?

Best regards,

--------------------
Fermín Galán Márquez
CTTC - Centre Tecnològic de Telecomunicacions de Catalunya
Parc Mediterrani de la Tecnologia, Av. del Canal Olímpic s/n, 08860
Castelldefels, Spain
Room 1.02
Tel : +34 93 645 29 12
Fax : +34 93 645 29 01
Email address: fermin dot galan at cttc dot es

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Re: [uml-devel] [uml-user] Hanging using 'iptables -L' in UML vm booted with con0=pts

[Blaisorblade]

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On giovedì 13 settembre 2007, Fermín Galán Márquez wrote:
> Dear Jeff,
>
> Jeff Dike wrote:
> > On Wed, Sep 12, 2007 at 11:52:32PM +0200, Fermín Galán Márquez wrote:
> >> This is the trace (as you can see I're repeated the experiment twice,
> >> the result is basically the same), hoping it could be useful to diagnose
> >> the problem and fix eventual bugs in the UML kernel. See below regarding
> >> the test procedure.
> >>
> >> (gdb) bt
> >> #0  0xb7f9d7f2 in ?? () from /lib/ld-linux.so.2
> >> #1  0xb7f19ab0 in tcsetattr () from /lib/i686/cmov/libc.so.6
> >> #2  0x080610d5 in generic_console_write (fd=7,
> >>     buf=0x828fc13 "ip_tables: (C) 2000-2006 Netfilter Core Team\n",
> >> n=45) at arch/um/drivers/chan_user.c:37
> >> #3  0x0806096e in console_write_chan (chans=0x82756f0,
> >>     buf=0x828fc13 "ip_tables: (C) 2000-2006 Netfilter Core Team\n",
> >> len=45) at arch/um/drivers/chan_kern.c:352
> >
> > Are you capturing UML output with a script or something?  This is the
> > signature of the script not reading from the pty, so everything just
> > backs up, waiting for the pty to clear up.
>
> AFAIK, no script is capturing (I understand you refers to the output of
> the UML linux executable) and, as a matter of fact, I'm getting some
> output when execute ./linux. To be precise, this is the exact command
> (and the output) I get:
>
> cibeles:/tmp# ./linux ubd0=/tmp/root_fs_debug con=null con0=pts
> uml_dir=/tmp umid=run
> Core dump limits :
>          soft - 0
>          hard - NONE
> Checking that ptrace can change system call numbers...OK
> Checking syscall emulation patch for ptrace...OK
> Checking advanced syscall emulation patch for ptrace...OK
> Checking for tmpfs mount on /dev/shm...OK
> Checking PROT_EXEC mmap in /dev/shm/...OK
> Checking for the skas3 patch in the host:
>    - /proc/mm...not found: No such file or directory
>    - PTRACE_FAULTINFO...not found
>    - PTRACE_LDT...not found
> UML running in SKAS0 mode
> [no more output, no new prompt]
>
> Then, in a second terminal in the host, I get the pts device and open a
> screen in the vm:
>
> cibeles:/tmp# uml_mconsole run/mconsole config con0
> Warning: couldn't stat file: /root/.uml/run/mconsole/mconsole - No such
> file or directory
> Warning: couldn't stat file: /tmp/uml/run/mconsole/mconsole - No such
> file or directory
> OK pts:/dev/pts/1
> cibeles:/tmp# screen /dev/pts/1
> [the terminal "goes into" the vm. I use it to cause the fail, as seen
> below] Debian GNU/Linux lenny/sid vm tty0
>
> vm login: root
> Password:
> Last login: Wed Sep 12 23:32:36 2007 on tty0
> Linux vm 2.6.22.4-xt-2m #1 Wed Sep 12 20:24:20 CEST 2007 i686
>
> The programs included with the Debian GNU/Linux system are free software;
> the exact distribution terms for each program are described in the
> individual files in /usr/share/doc/*/copyright.
>
> Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
> permitted by applicable law.
> vm:~# iptables -L
> [no output, linux process reach 100% CPU usage in the host]
>
> In a third host terminal I run gdb:
>
> cibeles:/tmp# cat run/pid
> 6627
> cibeles:/tmp# gdb ./linux 6627
>
> GNU gdb 6.4.90-debian
> Copyright (C) 2006 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you
> are welcome to change it and/or distribute copies of it under certain
> conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "i486-linux-gnu"...Using host libthread_db
> library "/lib/i686/cmov/libthread_db.so.1".
>
> Attaching to program: /tmp/linux, process 6627
> Reading symbols from /lib/i686/cmov/libutil.so.1...done.
> Loaded symbols for /lib/i686/cmov/libutil.so.1
> Reading symbols from /lib/i686/cmov/libc.so.6...done.
> Loaded symbols for /lib/i686/cmov/libc.so.6
> Reading symbols from /lib/ld-linux.so.2...done.
> Loaded symbols for /lib/ld-linux.so.2
> 0xb7f947f2 in ?? () from /lib/ld-linux.so.2
> (gdb) bt
> [showing the trace I've already sent in the other mail]
>
> Maybe there are "other outputs" apart of the output that the ./linux
> produces which could be causing the problem?

Please try logging in via SSH and reproducing the problem and the stacktrace, 
and also removing con=null - also have you double checked con=null is ok 
(maybe it was con=none, I'm not sure). I'm not sure screen is perfectly safe 
to use (it should be).
-- 
"Doh!" (cit.), I've made another mistake!
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade

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[uml-devel] (Solved) Hanging using 'iptables -L' in UML vm booted with con0=pts

[Fermín Galán Márquez]

Hi,

After some more debugging I think I've solved the problem (at least :) 
An explanation follows.

First, although apparently it seemed that the modules causing the 
problem were the ones related with networking (as David Fernández said 
in his mail) that assumption was wrong. In fact, the modules causing the 
problem are the ones that print some message in the "kernel message 
buffer" (I don't know what is the right name, but I'm referring to the 
message log that appears when the dmesg command is used) when modprobe 
load them. For example, ip_tables prints something like "ip_tables: (C) 
2000-2006 Netfilter Core Team".

The solution to the problem is using con1 instead of con0, I mean:

./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp umid=run

instead of

./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp umid=run

In that case you can 'iptables -L' works without problems.

Why? When the module is loaded it prints its message not only in the 
internal kernel message buffer but also in con0 (this can be checked 
running simply "./linux ubd0=/tmp/root_fs_debug", without con= 
redirectors). When con0 is redirected to null (con0=null) there is no 
problem, but if con0 is redirected to a pts (con0=pts) I guess that, in 
the moment of printing the message, some problem occurs with the output 
(as Jeff suggest in its mail) thus causing the vm hang.

This explains also why putting the module in /etc/modules works. The 
loading of the list of modules in /etc/modules is performed before UML 
assign virtual console to pts devices (the sequence can be checked 
observing the booting log).

I think that my solution is more a workaround that a definitive 
solution. Why when con0 is assigned to a pts modules can not (because of 
it hangs the vm) print its message but when it is assigned to null it 
works? Is there a bug in the UML kernel that need to be fixed? Or maybe 
the bug is in modprobe? I leave the question open for the experts in the 
UML internals... :)

Regarding the tests suggested by Paolo:

> Please try logging in via SSH and reproducing the problem and the stacktrace, 
> and also removing con=null - also have you double checked con=null is ok 
> (maybe it was con=none, I'm not sure). I'm not sure screen is perfectly safe 
> to use (it should be).

Do you really need that I perform these test or considers the report 
above is enough? If it's really needed I can do them, but it would take 
me some time (and maybe now it isn't a good idea because of they won't 
provide additional useful information :)

Best regards,

--------------------
Fermín Galán Márquez
CTTC - Centre Tecnològic de Telecomunicacions de Catalunya
Parc Mediterrani de la Tecnologia, Av. del Canal Olímpic s/n, 08860
Castelldefels, Spain
Room 1.02
Tel : +34 93 645 29 12
Fax : +34 93 645 29 01
Email address: fermin dot galan at cttc dot es

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Re: [uml-devel] (Workarounded) Hanging using 'iptables -L' in UML vm booted with con0=pts

[Paolo Giarrusso]

[-- Attachment #1.1: Type: text/plain, Size: 3480 bytes --]

On giovedì 13 settembre 2007, Fermín Galán Márquez wrote:
> Hi,
>
> After some more debugging I think I've solved the problem (at least :)
> An explanation follows.
>
> First, although apparently it seemed that the modules causing the
> problem were the ones related with networking (as David Fernández said
> in his mail) that assumption was wrong. In fact, the modules causing the
> problem are the ones that print some message in the "kernel message
> buffer" (I don't know what is the right name, but I'm referring to the
> message log that appears when the dmesg command is used) when modprobe
> load them. For example, ip_tables prints something like "ip_tables: (C)
> 2000-2006 Netfilter Core Team".

> The solution to the problem is using con1 instead of con0, I mean:
>
> ./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp umid=run
>
> instead of
>
> ./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp umid=run

This was con0=pts, I checked your other mail. Right?

> In that case you can 'iptables -L' works without problems.

> Why? When the module is loaded it prints its message not only in the
> internal kernel message buffer but also in con0 (this can be checked
> running simply "./linux ubd0=/tmp/root_fs_debug", without con=
> redirectors). When con0 is redirected to null (con0=null) there is no
> problem, but if con0 is redirected to a pts (con0=pts) I guess that, in
> the moment of printing the message, some problem occurs with the output
> (as Jeff suggest in its mail) thus causing the vm hang.

> This explains also why putting the module in /etc/modules works. The
> loading of the list of modules in /etc/modules is performed before UML
> assign virtual console to pts devices (the sequence can be checked
> observing the booting log).

> I think that my solution is more a workaround that a definitive
> solution. Why when con0 is assigned to a pts modules can not (because of
> it hangs the vm) print its message but when it is assigned to null it
> works? Is there a bug in the UML kernel that need to be fixed? Or maybe
> the bug is in modprobe? I leave the question open for the experts in the
> UML internals... :)
The problem does not lie in modprobe nor iptables - it is the behaviour of the 
system console wrt. the pts driver.

The only really strange thing is the 100% cpu usage - like if the operation 
were retried in a loop. And, well, there is a loop there - CATCH_EINTR (which 
I added)!

Now, what's unexpected is getting EINTR on that operation. That's really 
strange. However, I'll leave debugging to Jeff. If he cannot reproduce the 
problem he'll ask you more, I guess.

> Regarding the tests suggested by Paolo:
> > Please try logging in via SSH and reproducing the problem and the
> > stacktrace, and also removing con=null - also have you double checked
> > con=null is ok (maybe it was con=none, I'm not sure). I'm not sure screen
> > is perfectly safe to use (it should be).
>
> Do you really need that I perform these test or considers the report
> above is enough? If it's really needed I can do them, but it would take
> me some time (and maybe now it isn't a good idea because of they won't
> provide additional useful information :)

No, I just needed a proof that the problem was indeed with the output on a 
pts.

Thank you for you help
-- 
"Doh!" (cit.), I've made another mistake!
Paolo Giarrusso, aka Blaisorblade

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Re: [uml-devel] (Workarounded) Hanging using 'iptables -L' in UML vm booted with con0=pts

[Fermín Galán Márquez]

Dear Paolo,

>> The solution to the problem is using con1 instead of con0, I mean:
>>
>> ./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp umid=run
>>
>> instead of
>>
>> ./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp umid=run
> 
> This was con0=pts, I checked your other mail. Right?

Absolutely :)

Best regards,

--------------------
Fermín Galán Márquez
CTTC - Centre Tecnològic de Telecomunicacions de Catalunya
Parc Mediterrani de la Tecnologia, Av. del Canal Olímpic s/n, 08860
Castelldefels, Spain
Room 1.02
Tel : +34 93 645 29 12
Fax : +34 93 645 29 01
Email address: fermin dot galan at cttc dot es

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Re: [uml-devel] (Workarounded) Hanging using 'iptables -L' in UML vm booted with con0=pts

[David Fernández]

Hi,

Just a mail to confirm that this problem persists with new kernel 2.6.23.

I just downloaded and compiled 2.6.23 for UML
(http://www.dit.upm.es/vnuml/download/kernels/linux-2.6.23-1m.tar.bz2) and
tested that using "con0=pts" the virtual machines hang when loading kernel
modules that drop traces.

Using "con1=pts" the problem is solved, exactly as seen with previous kernel
versions.

Best regards,
David


  > -----Mensaje original-----
  > De: Fermín Galán Márquez [mailto:fermin.galan@cttc.es] 
  > Enviado el: miércoles, 19 de septiembre de 2007 21:42
  > Para: Paolo Giarrusso
  > CC: user-mode-linux-devel@lists.sourceforge.net; David Fernández
  > Asunto: Re: [uml-devel] (Workarounded) Hanging using 
  > 'iptables -L' in UML vm booted with con0=pts
  > 
  > Dear Paolo,
  > 
  > >> The solution to the problem is using con1 instead of 
  > con0, I mean:
  > >>
  > >> ./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp 
  > >> umid=run
  > >>
  > >> instead of
  > >>
  > >> ./linux ubd0=/tmp/root_fs_debug con=null con1=pts uml_dir=/tmp 
  > >> umid=run
  > > 
  > > This was con0=pts, I checked your other mail. Right?
  > 
  > Absolutely :)
  > 
  > Best regards,
  > 
  > --------------------
  > Fermín Galán Márquez
  > CTTC - Centre Tecnològic de Telecomunicacions de Catalunya 
  > Parc Mediterrani de la Tecnologia, Av. del Canal Olímpic 
  > s/n, 08860 Castelldefels, Spain Room 1.02 Tel : +34 93 645 
  > 29 12 Fax : +34 93 645 29 01 Email address: fermin dot 
  > galan at cttc dot es
  > 


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