Re: [PATCH 2/2] builtin/pack-objects.c: ensure pack validity from MIDX bitmap objects
Taylor Blau <me@ttaylorr.com> writes:
Show 23 quoted lines
> On Fri, May 13, 2022 at 04:06:39PM -0700, Jonathan Tan wrote:
> > (An alternative to the change in this patch may be to reset *found_pack
> > to NULL when it is found that the pack is invalid, but I haven't
> > investigated all the callers to see if they can tolerate *found_pack
> > moving changing non-NULL to NULL, so the change in this patch is
> > probably more practical.)
>
> I haven't either, but I think that this points out a flaw in the patch I
> originally posted.
>
> Consider this:
>
> - `want_object_in_pack()` calls `want_found_object()` with a pack that
> has gone away and has zero open fds, and `want_found_object()`
> returns -1
> - `want_object_in_pack()` continues and calls
> `want_object_in_pack_one()` later on, with some pack that is the
> same as `*found_pack`
> - `want_object_in_pack_one()` then _doesn't_ call `is_pack_valid()`
> (since `p == *found_pack`), leaving us in the same situation as
> before.
>
> I think that would be sufficient to hit this race even after this patch.
Ah, yes, indeed this would be a problem.
> I'll take a look to see if `want_object_in_pack()` callers can handle
> `*found_pack` being set back to NULL. They should be able to, but I want
> to do a little more careful analysis to be sure.
> Thanks for pointing this out, I am so glad for your review! :-)
Thanks for your kind words! Thanks for your explanations too.