From: Sam Delmerico Date: Fri, 05 Jan 2024 01:12:15 GMT Subject: Re: [PATCH] push: region_leave trace for negotiate_using_fetch Message-ID: In-Reply-To: * 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. Sam
On Wed, Jan 3, 2024 at 3:37 PM Junio C Hamano <gitster@pobox.com> wrote:
Sam Delmerico <delmerico@google.com> writes:

> There were two region_enter events for negotiate_using_fetch instead of
> one enter and one leave. This commit replaces the second region_enter
> event with a region_leave.
>
> Signed-off-by: Sam Delmerico <delmerico@google.com>
> ---
>  fetch-pack.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Looks right, after skimming a29263cf (fetch-pack: add tracing for
negotiation rounds, 2022-08-02).  Two questions and a half.

 * How did you find it?  Code inspection?  While writing a script to
   parse the output from around this area, your script noticed the
   ever-increasing nesting level?  Something else?

 * Would it be feasible to write some tests or tools that find
   similar problems (semi-)automatically?

 * Is the breakage (before this patch) something easily demonstrated
   in a new test in t/ somewhere?  And if so, would it be worth
   doing?

Thanks.  Will queue.


>
> diff --git a/fetch-pack.c b/fetch-pack.c
> index 31a72d43de..dba6d79944 100644
> --- a/fetch-pack.c
> +++ b/fetch-pack.c
> @@ -2218,7 +2218,7 @@ void negotiate_using_fetch(const struct oid_array *negotiation_tips,
>                                          the_repository, "%d",
>                                          negotiation_round);
>       }
> -     trace2_region_enter("fetch-pack", "negotiate_using_fetch", the_repository);
> +     trace2_region_leave("fetch-pack", "negotiate_using_fetch", the_repository);
>       trace2_data_intmax("negotiate_using_fetch", the_repository,
>                          "total_rounds", negotiation_round);
>       clear_common_flag(acked_commits);
>
> base-commit: a26002b62827b89a19b1084bd75d9371d565d03c