I don't see anything relevant that changed since commit: commit 664ccf245fcb343e1ea10e145bab3749423e9d0f Author: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> Date: Thu Mar 10 09:32:59 2016 -0500
Add tracepoint_disable_destructors() Calling this function from an instrumented program allows disabling tracepoint destructors. This allows threads to continue calling tracepoint code even after the tracepoint destructors have run. This is needed for applications that exit without joining all their threads. Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> CC: Jeffrey Chen <cp...@live.com> Can you point it out ? And let me know what is segfaulting, with a backtrace. I see that tracepoint_dlopen_ptr->tracepoint_unregister_lib(__start___tracepoints_ptrs) is still invoked from __tracepoints__ptrs_destroy() even if the disable destructors is set, but this only unregisters the library from the list of available events. I don't see how it would trigger a crash of threads still actively performing tracing. Thanks, Mathieu ----- On Sep 21, 2016, at 4:00 PM, Jeffrey Chen <cp...@live.com> wrote: > It seems that some changes went in recently that caused this workaround to not > work again. Originally, the __tracepoints__disable_destructors variable should > be checked around the beginning of the destructor functions ( > __tracepoints__destroy and __tracepoints__ptrs_destroy ), and return the > function when the variable is true. It is not in the beginning any more. So, > the segfault problem could happen. Is it possible to fix it again at your > convenience? Thanks a lot. > From: lttng-dev <lttng-dev-boun...@lists.lttng.org> on behalf of Mathieu > Desnoyers <mathieu.desnoy...@efficios.com> > Sent: Tuesday, March 15, 2016 12:00 PM > To: Jeffrey Chen > Cc: lttng-dev > Subject: Re: [lttng-dev] segfault when exiting process with background thread > Commit merged into master, thanks for your feedback! > Mathieu > ----- On Mar 15, 2016, at 2:48 PM, Jeffrey Chen <cp...@hotmail.com> wrote: >> Hi Mathieu: >> Will this fix be checked-in? Thanks. >> From: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> >> Sent: Thursday, March 10, 2016 3:27 PM >> To: Jeffrey Chen >> Cc: Jonathan Rajotte Julien; lttng-dev >> Subject: Re: segfault when exiting process with background thread >> ----- On Mar 10, 2016, at 5:59 PM, Jeffrey Chen <cp...@hotmail.com> wrote: >>> Thanks, Mathieu. >>> Yes, the fix works as a workaround. This is also the same workaround we have >>> now. >>> It seems the problem is due to a race condition, that it checked whether " >>> tracepoint_dlopen.rcu_read_lock_sym_bp " is not NULL. If not NULL, it calls >>> to >>> that. But, at this moment, memset cleared the memory. >>> This fix is okay with us, but I am not certain if it would break other >>> component, since I do not understand LTTng enough to tell. Thanks. >> In addition to memset clearing that memory, dlclose() of the >> lttng-ust-tracepoint >> shared object will clear the memory containing the called functions. >> Therefore, >> we need to skip both steps of the destructor if we want threads to survive >> after >> this destructor execution. >> Thanks, >> Mathieu >>> From: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> >>> Sent: Thursday, March 10, 2016 10:52 AM >>> To: Jeffrey Chen >>> Cc: Jonathan Rajotte Julien; lttng-dev >>> Subject: Re: segfault when exiting process with background thread >>> Hi Jeffrey, >>> I CC'd your @live.com address on the RFC patch. Please let me know if the >>> approach >>> is OK with you (and try it out). >>> See: >>> https://lists.lttng.org/pipermail/lttng-dev/2016-March/025608.html >>> Thanks, >>> Mathieu >>> ----- On Mar 10, 2016, at 1:35 PM, Jeffrey Chen <cp...@hotmail.com> wrote: >>>> 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.desnoy...@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.desnoy...@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-jul...@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 [ mailto:lttng-dev@lists.lttng.org | >>>>>>> lttng-dev@lists.lttng.org ] [ >>>>>>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev | >>>>>>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev ] >>>>>> -- >>>>>> Jonathan R. Julien >>>>>> Efficios >>>>>> _______________________________________________ >>>>>> lttng-dev mailing list >>>>>> lttng-dev@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@lists.lttng.org >>>>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev >>>> -- >>>> Mathieu Desnoyers >>>> EfficiOS Inc. >>>> http://www.efficios.com >>> -- >>> Mathieu Desnoyers >>> EfficiOS Inc. >>> http://www.efficios.com >> -- >> Mathieu Desnoyers >> EfficiOS Inc. >> http://www.efficios.com > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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