Re: [PATCH] push: region_leave trace for negotiate_using_fetch

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 5, 2024, 16:18 UTC
Message-ID: <xmqq4jfrpxce.fsf@gitster.g>
In-Reply-To: <CAHVcGPSSJr7L_NyFSKEkEywBap6hUrucga98RLpa6xuZ0k4CzA@mail.gmail.com>

Sam Delmerico <delmerico@google.com> writes:

Show 22 quoted lines

> * 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.