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

[Jeffrey Chen]

Thanks Mathieu.

Is there a plan at LTTng side to fix this issue? If so, we could wait for the fix. If not, we will have to workaround the problem for now (probably by applying your fix ourselves). Thanks.



________________________________
From: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Sent: Tuesday, March 8, 2016 6:09 PM
To: Jonathan Rajotte Julien
Cc: lttng-dev
Subject: Re: [lttng-dev] segfault when exiting process with background thread

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







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--
Jonathan R. Julien
Efficios

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

_______________________________________________
lttng-dev mailing list
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--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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