[ltt-dev] Kernel Oops during lttctl_start()

[Mathieu Desnoyers]

* 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

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com