[ltt-dev] Kernel Oops during lttctl_start()

[Bernd.Hufmann@ericsson.com (Bernd Hufmann)]

Hi Mathieu

Thank you very much for looking at the problem and for providing a fix. 
Unfortunately, I won't be able to test the fix any time soon, because it 
requires to compile and install a new kernel on my virtual machine which 
can take some time. When it is integrated in a later LTTng PPA release 
for Ubuntu I will be able to give it a try.

Best Regards
Bernd

On 04/18/2011 10:12 PM, Mathieu Desnoyers wrote:
> * Mathieu Desnoyers (compudj at krystal.dyndns.org) wrote:
>> * Bernd Hufmann (Bernd.Hufmann at ericsson.com) wrote:
> [...]
>>> Steps to reproduce:
>>>      - Enable all markers (use ltt-armall)
>>>      - Start tcf-client
>>>      - connect<remote>
>>>      - tcf ltt_control setupTrace "kernel" "0" "h2"
>>>      - tcf ltt_control setChannelEnable "kernel" "0" "h2" false
>>>      - tcf ltt_control allocTrace "kernel" "0" "h2"
>>>      - lttctl_client ltt_control writeTraceLocal "kernel" "0" "h2"
>>> "/tmp/h2" 2 false false false
>>>      - tcf ltt_control startTrace "kernel" "0" "h2"
>>>
>>> Now, the command startTrace won't return. It hangs on line "if
>>> (write(fd, op, strlen(op)) == -1)" of method "lttctl_sendop()" which was
>>> called by method "lttctl_start()" (see file liblttctrl.c). Please see
>>> attached file "dmesg_start.log" for the dmesg output.
>>>
>> [...]
>>> [  416.740678] LTT : Tracing not active for trace h5
>>> [  416.740908] LTT state dump begin
>>> [  416.740931] LTT state dump thread start
>>> [  416.743693] LTT state dump end
>>> [  447.956279] LTT: 36 events written in channel metadata (cpu 0, index 0)
>>> [  447.956424] LTT: 54278 events written in channel fs (cpu 0, index 0)
>>> [  447.956468] LTT: 40989 events written in channel fs (cpu 0, index 1)
>>> [  618.382904] LTT : Tracing not active for trace h6
>>> [  618.383350] BUG: unable to handle kernel NULL pointer dereference at 00000014
>>> [  618.383983] IP: [<e080828f>] ltt_trace_start+0x7f/0x190 [ltt_tracer]
>> This looks like a bug in lttng-modules (the LTTng kernel modules).
>> Probably a bug with the way the current LTTng-stable versions handle the
>> trace session "templates". The good news is that we are getting rid of
>> all that code in the upcoming LTTng (with UST/ltt-sessiond/CTF
>> integration), so this bug is very likely to vanish then.
>>
>> I'll try to have a look.
>>
>> Thanks for reporting this.
> It should be fixed in the lttng-modules.git tree v0.19-stable branch now
> (commit e5b34c668a7d7b8aeab9fa2bdbb31eed4eff7929). Can you try again
> using this version of lttng-modules and confirm that it fixes your crash
> before I post a new lttng-modules v0.19-stable release ?
>
> Thanks,
>
> Mathieu
>