LTTng » LTTng-modules

When doing repeated short lived live kernel tracing sessions, the output of lttng list -k is sometimes corrupted (the loglevel value seems random) or some events are missing.

Versions :
lttng-modules : 2.4.0-rc4 309370e252e189867745fb31fe5c15c9ff494f34
lttng-tools : 2.4.0-rc5 1d6448a074accdc6cb32e2f724f9768b006a6d67

Steps to reproduce :
- Compile lttngtop
- in utils/lttngtrace, check where the "$SUDO lttng list k" is called and add an exit in the if statement below that (to have a clean exit when the problem appears)
while true; do ./utils/lttngtrace ls; done

After less than 2 minutes, you should see the error message printed in loop.

It will stay in the corrupted state until you let lttngtrace continue (removing the exit in the if statement).

A copy of the corrupted lttng list -k is attached to this bug.

No change in the list of loaded modules has been noticed.
The lttng-sessiond, consumer and relay don't restart between runs of lttngtrace.

Basically, lttngtrace creates a live session with a set of events and contexts; attach to it with a client and destroys the session.
There might be something related to the list of enabled events and/or contexts, because reproducing this with only sched_switch enabled does not seem to reproduce the problem.