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From: "René Scharfe" <l.s.r@web.de>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Junio C Hamano <gitster@pobox.com>,
	Git List <git@vger.kernel.org>, Taylor Blau <me@ttaylorr.com>,
	Christian Couder <chriscool@tuxfamily.org>,
	Jeff King <peff@peff.net>
Subject: Re: [PATCH v2 3/3] Revert "pack-objects: lazily set up "struct rev_info", don't leak"
Date: Mon, 28 Nov 2022 15:29:42 +0100	[thread overview]
Message-ID: <c5aeb93c-763d-3eae-0150-15f6ca675319@web.de> (raw)
In-Reply-To: <221128.864jujmhgp.gmgdl@evledraar.gmail.com>

Am 28.11.2022 um 12:31 schrieb Ævar Arnfjörð Bjarmason:
>
> 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?

I have no idea how to stop get_object_list() from using struct rev_info.
We could let it take a struct list_objects_filter_options pointer
instead and have it build a struct rev_info internally, but that would
just move the problem, not solve 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.

Well, that TODO fix should remove this new diff_free() call, but I
agree that this is fragile.

Removing the "TEST_PASSES_SANITIZE_LEAK=true" line from affected tests
is probably better.

> As you'd see if you made release_revisions() simply call
> diff_free(&revs.diffopt) doing so would reveal some really gnarly edge
> cases.

That was my first attempt; it breaks lots of tests due to double frees.

> I haven't dug into this one, but offhand I'm not confident in saying
> that this isn't exposing us to some aspect of that gnarlyness (maybe
> not, it's been a while since I looked).

I saw it as the way towards a release_revisions() that calls diff_free()
itself: Add such calls to each of them, fix the "gnarlyness"
individually, finally move them all into release_revisions().  The only
problem is that there are 60+ callsites.

> (IIRC some of the most gnarly edge cases will only show up as CI
> failures on Windows, to do with the ordering of when we'll fclose()
> files hanging off that "diffopt").

Fun.

René

  parent reply	other threads:[~2022-11-28 14:31 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-12 10:42 [PATCH 0/3] pack-objects: fix and simplify --filter handling René Scharfe
2022-11-12 10:44 ` [PATCH 1/3] pack-objects: fix handling of multiple --filter options René Scharfe
2022-11-12 11:41   ` Ævar Arnfjörð Bjarmason
2022-11-13 17:31     ` René Scharfe
2022-11-12 16:58   ` Jeff King
2022-11-13  5:01     ` Taylor Blau
2022-11-13 16:44       ` Jeff King
2022-11-13 17:31       ` René Scharfe
2022-11-12 10:44 ` [PATCH 2/3] pack-object: simplify --filter handling René Scharfe
2022-11-12 11:45   ` Ævar Arnfjörð Bjarmason
2022-11-12 17:02   ` Jeff King
2022-11-13 16:49     ` Jeff King
2022-11-13 17:31     ` René Scharfe
2022-11-12 10:46 ` [PATCH 3/3] list-objects-filter: remove OPT_PARSE_LIST_OBJECTS_FILTER_INIT() René Scharfe
2022-11-20 10:03 ` [PATCH v2 0/3] pack-objects: fix and simplify --filter handling René Scharfe
2022-11-20 10:06   ` [PATCH v2 1/3] t5317: stop losing return codes of git ls-files René Scharfe
2022-11-20 10:07   ` [PATCH v2 2/3] t5317: demonstrate failure to handle multiple --filter options René Scharfe
2022-11-20 10:13   ` [PATCH v2 3/3] Revert "pack-objects: lazily set up "struct rev_info", don't leak" René Scharfe
2022-11-28 10:03     ` Junio C Hamano
2022-11-28 11:12       ` Ævar Arnfjörð Bjarmason
2022-11-28 12:00         ` [PATCH] t5314: check exit code of "rev-parse" Ævar Arnfjörð Bjarmason
2022-11-28 13:51           ` René Scharfe
2022-11-28 14:18           ` [PATCH v2] t5314: check exit code of "git" Ævar Arnfjörð Bjarmason
2022-11-28 11:26       ` [PATCH v2 3/3] Revert "pack-objects: lazily set up "struct rev_info", don't leak" René Scharfe
2022-11-28 11:31         ` Ævar Arnfjörð Bjarmason
2022-11-28 12:24           ` Ævar Arnfjörð Bjarmason
2022-11-28 15:16             ` René Scharfe
2022-11-28 15:27               ` Ævar Arnfjörð Bjarmason
2022-11-28 14:29           ` René Scharfe [this message]
2022-11-28 14:34             ` Ævar Arnfjörð Bjarmason
2022-11-28 15:56               ` René Scharfe
2022-11-28 17:57                 ` René Scharfe
2022-11-28 18:32                   ` Ævar Arnfjörð Bjarmason
2022-11-28 21:57                     ` René Scharfe
2022-11-29  1:26                       ` Jeff King
2022-11-29  1:46                         ` Junio C Hamano
2022-11-29 10:25                         ` Ævar Arnfjörð Bjarmason
2022-11-29  7:12                       ` Ævar Arnfjörð Bjarmason
2022-11-29 19:18                         ` René Scharfe
2022-11-28 17:57                 ` Ævar Arnfjörð Bjarmason
2022-11-22 19:02   ` [PATCH v2 0/3] pack-objects: fix and simplify --filter handling Jeff King
2022-11-29 12:19 ` [PATCH v3 0/5] " René Scharfe
2022-11-29 12:21   ` [PATCH v3 1/5] t5317: stop losing return codes of git ls-files René Scharfe
2022-11-29 12:22   ` [PATCH v3 2/5] t5317: demonstrate failure to handle multiple --filter options René Scharfe
2022-11-29 12:23   ` [PATCH v3 3/5] pack-objects: fix handling of " René Scharfe
2022-11-30  1:09     ` Junio C Hamano
2022-11-30  7:11       ` René Scharfe
2022-11-29 12:25   ` [PATCH v3 4/5] pack-objects: simplify --filter handling René Scharfe
2022-11-29 13:27     ` Ævar Arnfjörð Bjarmason
2022-11-30 11:23       ` René Scharfe
2022-11-29 12:26   ` [PATCH v3 5/5] list-objects-filter: remove OPT_PARSE_LIST_OBJECTS_FILTER_INIT() René Scharfe
2022-11-30  1:20     ` Junio C Hamano

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