Re: [PATCH] commit-graph: avoid leaking topo_levels slab in write_commit_graph()

From: Andrzej Hunt <andrzej@ahunt.org>
Date: Feb 22, 2021, 19:14 UTC
Message-ID: <dfc713c2-c5f6-6c7f-230b-810da0e39ebf@ahunt.org>
In-Reply-To: <6ef5487b-905d-8f34-a53c-d1138f5528d9@gmail.com>

On 22/02/2021 15:15, Derrick Stolee wrote:

> This change looks like a sane change to me. It definitely fixes a leak.
> The leak "wasn't hurting anybody" because write_commit_graph() is only
> called at most once per process, and the process closes itself out
> shortly after. Still, it's good to have good memory hygiene here.

Good to know - thank you! As I become more familiar with git, I'm beginning to realise that most leaks are unlikely to be much importance (even though I personally err on the side of fixing any and all issues).

One thing I forgot to mention: in this specific case the leak was causing a build failure when trying to build git's fuzzers within oss-fuzz locally*. Specifically the following command would fail (see also fuzz failure reproduction instructions which describe the setup [1]).

  $ python infra/helper.py build_fuzzers --sanitizer address git

As far as I can tell the issue is that: a copy of git built with ASAN is used to produce the fuzzing corpus as part of the git-specific build script [2] - the leak warning causes the script to fail. (It's possible to argue that the build script should disable ASAN's leak checking when running git, via detect_leaks=0 to reduce the risk of such breakage - I may try to suggest such a change to oss-fuzz.)

ATB,
   Andrzej

* Given that oss-fuzz is building via docker, I would intuitively 
suspect that the same issue occurs in automation - I'm not sure how to 
verify this myself.

[1] https://google.github.io/oss-fuzz/advanced-topics/reproducing/#building-using-docker [2] https://github.com/google/oss-fuzz/blob/1b0115eefd70491376cf3cb6f88e49632c78ee18/projects/git/build.sh#L37