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

>
> On Mon, Nov 28 2022, René Scharfe wrote:
>
>> Am 28.11.2022 um 11:03 schrieb Junio C Hamano:
>>> René Scharfe <l.s.r@web.de> writes:
>>>
>>>> This reverts commit 5cb28270a1ff94a0a23e67b479bbbec3bc993518.
>>>>
>>>> 5cb28270a1 (pack-objects: lazily set up "struct rev_info", don't leak,
>>>> 2022-03-28) avoided leaking rev_info allocations in many cases by
>>>> calling repo_init_revisions() only when the .filter member was actually
>>>> needed, but then still leaking it.  That was fixed later by 2108fe4a19
>>>> (revisions API users: add straightforward release_revisions(),
>>>> 2022-04-13), making the reverted commit unnecessary.
>>>
>>> Hmph, with this merged, 'seen' breaks linux-leaks job in a strange
>>> way.
>>>
>>> https://github.com/git/git/actions/runs/3563546608/jobs/5986458300#step:5:3917
>>>
>>> Does anybody want to help looking into it?
>
> [I see we crossed E-Mails]:
> https://lore.kernel.org/git/221128.868rjvmi3l.gmgdl@evledraar.gmail.com/
>
>> The patch exposes that release_revisions() leaks the diffopt allocations
>> as we're yet to address the TODO added by 54c8a7c379 (revisions API: add
>> a TODO for diff_free(&revs->diffopt), 2022-04-14).
>
> That's correct, and we have that leak in various places in our codebase,
> but per the above side-thread I think this is primarily exposing that
> we're setting up the "struct rev_info" with your change when we don't
> need to. Why can't we just skip it?

> Yeah, if we do set it up we'll run into an outstanding leak, and that
> should also be fixed (I have some local patches...), but the other cases
> I know of where we'll leak that data is where we're actually using the
> "struct rev_info".
>
> I haven't tried tearing your change apart to poke at it myself, and
> maybe there's some really good reason for why you can't separate getting
> rid of the J.5.7 dependency and removing the lazy-init.
>
>> The patch below plugs it locally.
>>
>> --- >8 ---
>> Subject: [PATCH 4/3] fixup! revision: free diffopt in release_revisions()
>>
>> Signed-off-by: René Scharfe <l.s.r@web.de>
>> ---
>>  builtin/pack-objects.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
>> index 3e74fbb0cd..a47a3f0fba 100644
>> --- a/builtin/pack-objects.c
>> +++ b/builtin/pack-objects.c
>> @@ -4462,6 +4462,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
>>  	} else {
>>  		get_object_list(&revs, rp.nr, rp.v);
>>  	}
>> +	diff_free(&revs.diffopt);
>>  	release_revisions(&revs);
>>  	cleanup_preferred_base();
>>  	if (include_tag && nr_result)
>
> So, the main motivation for the change was paranoia that a compiler or
> platform might show up without J.5.7 support and that would bite us, but
> we're now adding a double-free-in-waiting?
>
> I think we're both a bit paranoid, but clearly have different
> paranoia-priorities :)
>
> If we do end up with some hack like this instead of fixing the
> underlying problem I'd much prefer that such a hack just be an UNLEAK()
> here.
>
> I.e. we have a destructor for "revs.*" already, let's not bypass it and
> start freeing things from under it, which will result in a double-free
> if we forget this callsite once the TODO in 54c8a7c379 is addressed.