add-context fails silently with perf_event_paranoid=4, no trace produced
A disallowed add-context (e.g. because of perf_event_paranoid) produces an error message and a non-zero exit code.
A disallowed add-context produces only a message in the system log, invisible to the normal user.
For example, when perf_event_paranoid forbids it you get a message of the form:
Error: UST app create channel context failed for app (pid: 76220) with ret -1024
But the only effects observable to the user are:
- no trace is produced, and
- when you destroy the session there is a message like
Failed to perform a quiet rotation as part of the destruction of session "..."
If other users are like me they will spend quite some time trying to figure out what is wrong in their code, setup etc. before figuring out what's wrong (or having someone on IRC identify it for them, as in my case).
This is Ubuntu 20.04.1, with lttng-ust 2.11.0
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