[lttng-dev] lost trace events

[Alok Priyadarshi]

A custom trace event class emits "begin" and "end" events in its
constructor and destructor respectively. So I do not think this is due to
conditional path.

Sequence of commands to capture a snapshot are:
lttng create --snapshot
lttng enable-event --userspace --all
lttng add-context --userspace -t vpid -t vtid
lttng start
lttng stop
lttng snapshot record

We create a new session for each snapshot to make sure that the buffer does
not have any left-over events from the previous session. But I am curious
if lttng shares buffers between sessions or re-uses buffers from an old
session without flushing?

Note that I am using the default LTTNG_BUFFER_PER_UID mode. All processes
for our application run under one UID, and only one tracing session is
active at a time.

On Wed, Nov 7, 2018 at 12:09 PM Jonathan Rajotte-Julien <
jonathan.rajotte-julien at efficios.com> wrote:

> Hi Alok,
>
> On Wed, Nov 07, 2018 at 11:53:25AM -0800, Alok Priyadarshi wrote:
> > Hi Jonathan,
> >
> > Thanks for your response.
> >
> > We are tracing function scopes. Each scope emits two events - begin and
> > end. We noticed that some begin events did not have corresponding end
> > events in the trace.
>
> Seems like a solid ground as long as the corresponding ending event is not
> inside any conditional paths. I'm sure you already validated that but we
> never
> know.
>
> >
> > I have the trace with this problem available. Would that provide any
> clue?
>
> It could help but I presume it might contains confidential or sensible
> information. Let's define the scenario first and we will go back to actual
> trace data if needed.
>
> > If not, I will try to extract a small reproducer.
>
> That would be best. In the meantime, could you provide the exact lttng
> commands
> used to setup everything and describe subsequent lttng commands used for
> snapshot etc.
>
> You can omit event name or replace them with dummy name if necessary.
>
> Cheers
>
> --
> Jonathan Rajotte-Julien
> EfficiOS
>
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