[lttng-dev] segfault when exiting process with background thread

[Mathieu Desnoyers]

The attached patch works around the issue. The problem is 
the tracepoint destructors that run in parallel with the thread 
that still exists. 

If we remove this, we leak the liblttng-ust-tracepoint.so.0 shared 
object on dlclose of the instrumented code. Not sure if we should 
care though... 

Thoughts ? 

Thanks, 

Mathieu 

----- On Mar 8, 2016, at 7:35 PM, Mathieu Desnoyers <mathieu.desnoyers at efficios.com> wrote: 

> Reproduced it on master (ust and tools).

> Repro with:

> lttng create
> lttng enable-event -u -a
> lttng start

> then run hello a few times, it eventually segfaults in the spawned thread.

> Looking into it.

> Thanks,

> Mathieu

> ----- On Mar 8, 2016, at 7:12 PM, Jonathan Rajotte Julien
> <Jonathan.rajotte-julien at efficios.com> wrote:

>> Hi Jeffrey,

>> Could you provide the version for lttng-ust, lttng-tools, lttng-modules (if
>> installed)?

>> Were you able to reproduce the issue on master (git) ?

>> What are the exact order of command to reproduce the problem ?

>> Thanks

>> On 2016-03-08 06:43 PM, Jeffrey Chen wrote:

>>> Hi LTTng community:

>>> We are using LTTng for our production environment. We have been noticing
>>> segfault problem when our process exit. We think the problem is due to the
>>> background thread continue to write traces, while LTTng cleanup its memory. We
>>> do not know how to fix this issue without changing LTTng code base. I have
>>> written a very simple app that could repro the problem. Most of my codes are
>>> copy pasted from the LTTng doc sample. Is there any fix that the LTTng side
>>> could do?

>>> hello.c

>>> #include <stdio.h>
>>> #include "hello-tp.h"
>>> #include <pthread.h>

>>> void* doSomeThing(void *arg)
>>> {
>>> int x;
>>> for (x = 0; x < 100000; ++x) {
>>> tracepoint(hello_world, my_first_tracepoint, x, "test");
>>> }
>>> }

>>> int main(int argc, char *argv[])
>>> {
>>> int x;

>>> getchar();

>>> pthread_t inc_x_thread;

>>> if(pthread_create(&inc_x_thread, NULL, doSomeThing, NULL)) {

>>> fprintf(stderr, "Error creating thread\n");
>>> return 1;
>>> }

>>> tracepoint(hello_world, my_first_tracepoint, 23, "hi there!");

>>> return 0;
>>> }

>>> hello-tp.c

>>> #define TRACEPOINT_CREATE_PROBES
>>> #define TRACEPOINT_DEFINE

>>> #include "hello-tp.h"

>>> hello-tp.h

>>> #undef TRACEPOINT_PROVIDER
>>> #define TRACEPOINT_PROVIDER hello_world

>>> #undef TRACEPOINT_INCLUDE
>>> #define TRACEPOINT_INCLUDE "./hello-tp.h"

>>> #if !defined(_HELLO_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ)
>>> #define _HELLO_TP_H

>>> #include <lttng/tracepoint.h>

>>> TRACEPOINT_EVENT(
>>> hello_world,
>>> my_first_tracepoint,
>>> TP_ARGS(
>>> int, my_integer_arg,
>>> char*, my_string_arg
>>> ),
>>> TP_FIELDS(
>>> ctf_string(my_string_field, my_string_arg)
>>> ctf_integer(int, my_integer_field, my_integer_arg)
>>> )
>>> )

>>> #endif /* _HELLO_TP_H */

>>> #include <lttng/tracepoint-event.h>

>>> Compile

>>> gcc -c -I. hello-tp.c
>>> gcc -c hello.c
>>> gcc -o hello hello.o hello-tp.o -llttng-ust -ldl -lpthread

>>> _______________________________________________
>>> lttng-dev mailing list lttng-dev at lists.lttng.org
>>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

>> --
>> Jonathan R. Julien
>> Efficios

>> _______________________________________________
>> lttng-dev mailing list
>> lttng-dev at lists.lttng.org
>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

-- 
Mathieu Desnoyers 
EfficiOS Inc. 
http://www.efficios.com 
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