On 2022.05.03 10:59, Jeff Hostetler wrote:
>
>
> On 4/28/22 5:46 PM, Junio C Hamano wrote:
> > Josh Steadmon <steadmon@xxxxxxxxxx> writes:
> >
> > > In rare cases, wait_or_whine() cannot determine a child process's exit
> > > status (and will return -1 in this case). This can cause Git to issue
> > > trace2 child_exit events despite the fact that the child is still
> > > running.
>
> I'm curious what is causing the spurious return values.
> Could you instrument wait_or_whine() and see which of the
> if/else arms are causing the -1 to be returned?
>
> That routine is rather complicated and looks like it has 3
> different ways that a -1 could be returned.
Unfortunately we haven't been able to reproduce the issue, so
instrumentation won't clarify the cause unless we randomly hit another
instance.
> >
> > Rather, we do not even know if the child is still running when it
> > happens, right? It is curious what "rare cases" makes the symptom
> > appear. Do we know?
> >
> > The patch looks OK from the "we do not know the child exited in this
> > case, so we shouldn't be reporting the child exit" point of view, of
> > course. Having one event that started a child in the log and then
> > having millions of events that reports the exit of the (same) child
> > is way too broken. With this change, we remove these phoney exit
> > events from the log.
> >
> > Do we know, for such a child process that caused these millions
> > phoney exit events, we got a real exit event at the end? Otherwise,
> > we'd still have a similar problem in the opposite direction, i.e. a
> > child has a start event recorded, many exit event discarded but the
> > log lacks the true exit event for the child, implying that the child
> > is still running because we failed to log its exit?
> >
> > > int finish_command_in_signal(struct child_process *cmd)
> > > {
> > > int ret = wait_or_whine(cmd->pid, cmd->args.v[0], 1);
> > > - trace2_child_exit(cmd, ret);
> > > + if (ret != -1)
> > > + trace2_child_exit(cmd, ret);
> > > return ret;
> > > }
>
> Since this is only called from pager.c and is used to setup the
> pager, I have to wonder if you're only getting these spurious events
> for the pager process or for any of the other random child processes.
>
> And whether they are received while the pager is alive and working
> properly, or when you're trying to quit the pager or when the pager
> is trying to signal eof.
It was for a pager run by `git diff`. The only other child process in
this instance was `git status`. I believe the events were generated
while the user was not interacting with the process; IIRC the pager was
left running in a terminal overnight and they discovered the next
morning that their disk was filled up by trace logs.
