Re: [PATCH] push: region_leave trace for negotiate_using_fetch

Sam Delmerico [off-list ref] writes:

* I don't exactly remember how I noticed it. I was doing some
debugging around the push negotiation code and either 1) saw this
region get entered twice in the trace output, or 2) I was just reading
the code around here and saw two enters.

* Perhaps there could be a check before the last git process ends that
checks that all opened trace regions have been closed? I'm not sure
how much work this would involve. It's probably also not a very
proactive way to catch these bugs since it would only get triggered
when a *user* hits a code path with a trace region that never exits.

* There could also be a test that checks that every region_enter trace
log has a corresponding region_leave. But I'm not sure how to ensure
that every code path is checked.

Overall, I'm not sure how much benefit there is from checking for
this. I'm not sure that it would have a large impact if it were to
happen again. For example, I think that it could be noticed relatively
quickly by a person/system looking at metrics like I was (e.g. if the
time spent in a region is infinite or zero).

FWIW I didn't see any other examples of this when going through logs.

The above matches my intuition.  A test that covers this specific
case would likely be of low value as it is unlikely for us to
regress this specific one.  A CI job that runs all the tests under
tracing and inspects the log may catch some but its finding would be
limited to the code paths that are covered (but increasing the test
coverage would help here, not just for finding unbalanced region
markers, but for finding bugs in general).

Thanks.