[lttng-dev] Crash on first run of target using liblttng-ust-cyg-profile.so, but subsequent runs succeed

[Mathieu Desnoyers]

---- On Feb 11, 2016, at 9:01 AM, Sean Heelan <seanheelan at gmail.com> wrote: 

> Hi all,
> I am running a target within a Docker instance, and tracing function execution
> using the latest LTTng release (2.7). The commands I am issuing look as
> follows:

> ----
> lttng create cc_session -o bla
> lttng enable-event --userspace lttng_ust_cyg_profile:func_entry
> lttng start

> LD_PRELOAD=liblttng-ust-cyg-profile.so target

> lttng stop
> lttng destroy
> ----

> When the target is executed it aborts with the following error:

> ----
> php: lttng-ust-comm.c:1582: lttng_ust_init: Assertion `!ret' failed.
> ----

> If I rerun the command it then works fine. In fact, simply doing the following
> within the Docker container demonstrates the issue:

> ----
> LD_PRELOAD=liblttng-ust-cyg-profile.so ls
> LD_PRELOAD=liblttng-ust-cyg-profile.so ls
> ----

> The first 'ls' will fail at the same point mentioned above, while the second
> will succeed. Off the top of my head I'm struggling to come up with an
> explanation as to what impact the first execution using LD_PRELOAD would have
> on the second. Does it impact a shared lib cache in some way, which I'm unaware
> of?

> Any assistance would be appreciated!

It appears that sem_timedwait() returns an unexpected error. 

Can you add a ERROR("sem_timedwait"); just before the assert at line 1582 in your liblttng-ust/lttng-ust-comm.c 
and show us the output ? 

Also, what is the value of your LTTNG_UST_REGISTER_TIMEOUT env. var. ? 

Thanks, 

Mathieu 

> Sean

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