On Wed, 12 Aug 2020 16:58:54 -0400 Steven Rostedt rostedt@goodmis.org wrote:
This is marked as "Fixes" but is more of a clean up than a true fix. Backport if you want, but its not critical.
A note to stable maintainers. I originally thought this was just a clean up, but it was then found that it actually does fix a bug.
I cut out the explanation in the email:
This addresses an issue we've seen with users trying to change current_tracer when they happen to have rasdaemon installed. rasdaemon uses the trace_pipe interface at runtime, which therefore blocks changing the current tracer. But of course, unless you know about rasdaemon internals, it isn't exactly an obvious failure mode.
Conflict in __remove_instance() was due to a change in reference counter semantics introduced later in v5.5 via commit 288797871473 "tracing: Adding new functions for kernel access to Ftrace instances". Resolved by leaving the first test in the if statement as it was in v5.4.
-- Steve