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

[Mathieu Desnoyers]

----- On Feb 12, 2016, at 3:21 PM, Mathieu Desnoyers <mathieu.desnoyers at efficios.com> wrote: 

> ----- On Feb 12, 2016, at 12:02 PM, Mathieu Desnoyers
> <mathieu.desnoyers at efficios.com> wrote:

>> ---- 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. ?

> Also, what architecture, Linux distribution, and kernel
> version are you using ?

I pushed the following fix in lttng-ust: 

commit 5cf81d53e305c81517e48e0dc91620a916cdc0cc 
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com> 
Date: Fri Feb 12 15:44:10 2016 -0500 

Fix: handle negative range for LTTNG_UST_REGISTER_TIMEOUT 

We should not consider values below -1 as valid timeout values, this is 
is unexpected and could lead to EINVAL errors returned by sem_timedwait. 

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com> 

Let me know if it helps, 

Thanks, 

Mathieu 

> Thanks,

> Mathieu

>> Thanks,

>> Mathieu

>>> Sean

>>> _______________________________________________
>>> 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

> _______________________________________________
> 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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