Re: [PATCH v2 3/3] Revert "pack-objects: lazily set up "struct rev_info", don't leak"

[Jeff King <peff@peff.net>]

On Mon, Nov 28, 2022 at 10:57:02PM +0100, René Scharfe wrote:

> >> diff --git a/revision.c b/revision.c
> >> index 439e34a7c5..6a51ef9418 100644
> >> --- a/revision.c
> >> +++ b/revision.c
> >> @@ -3055,6 +3055,7 @@ void release_revisions(struct rev_info *revs)
> >>  	release_revisions_mailmap(revs->mailmap);
> >>  	free_grep_patterns(&revs->grep_filter);
> >>  	/* TODO (need to handle "no_free"): diff_free(&revs->diffopt) */
> >> +	FREE_AND_NULL(revs->diffopt.parseopts);
> >>  	diff_free(&revs->pruning);
> >>  	reflog_walk_info_release(revs->reflog_info);
> >>  	release_revisions_topo_walk_info(revs->topo_walk_info);
> >
> > At this point I'm unclear on what & why this is needed? I.e. once we
> > narrowly fix the >1 "--filter" options what still fails?
> 
> As I wrote: A call to an initialization function followed by a call to a
> cleanup function and nothing else shouldn't leak.  There are examples of
> repo_init_revisions()+release_revisions() without setup_revisions() or
> diff_setup_done() beyond pack-objects.  I mentioned prune, but there are
> more, e.g. in sequencer.c.

I tend to agree with you; an init+release combo should release all
memory. We _can_ work around it in the caller here, but I think we are
better to correct the root cause.

I do think what Ævar is saying is: once we have fixed the bug, why are
more changes needed? I.e., why would we get rid of the lazy-init. IMHO
the answer is that the lazy-init is a more complex pattern, and requires
more boilerplate code (which can lead to more bugs, as we saw). So once
the bug is fixed, this is purely about cleanup/simplification (if one
ignores the C-standard issues), but I tend to think it is one worth
doing.

(Apologies to Ævar if I'm mis-stating your position).

> > But in general: I don't really think this sort of thing is worth
> > it. Here we're reaching into a member of "revs->diffopt" behind its back
> > rather than calling diff_free(). I think we should just focus on being
> > able to do do that safely.
> 
> Sure, but the FREE_AND_NULL call is simple and safe, while diff_free()
> is complicated and calling it one time too many can hurt.

Again, I'd agree with you here. In the long run, yes, we want
diff_free(). But if that is not ready yet, the FREE_AND_NULL() is a
stepping stone that takes us in the right direction and which we can do
immediately.

> > WIP patches I have in that direction, partially based on your previous
> > "is_dead" suggestion:
> >
> > 	https://github.com/avar/git/commit/e02a15f6206
> > 	https://github.com/avar/git/commit/c718f36566a
> 
> Copy-typed the interesting parts of the first patch like a medieval monk
> because there doesn't seem to be a download option. :-|

This is the actual reason I responded to your message. ;) Try:

  https://github.com/avar/git/commit/e02a15f6206.patch

etc. I don't think there's a "raw patch" link or similar in the
interface, though. You have to just know about it.

-Peff