Re: [PATCH] repository: fix free problem with repo_clear(the_repository)

From: Stefan Beller <sbeller@google.com>
Date: May 9, 2018, 17:50 UTC
Message-ID: <CAGZ79kbFiULj1NJARm6ObYrqv_Fu+U2sb8h_sNJwdWur+JqrvQ@mail.gmail.com>
In-Reply-To: <20180509170409.13666-1-pclouds@gmail.com>

On Wed, May 9, 2018 at 10:04 AM, Nguyễn Thái Ngọc Duy <pclouds@gmail.com> wrote:

> the_repository is special. One of the special things about it is that
> it does not allocate a new index_state object like submodules but
> points to the global the_index variable instead. As a global variable,
> the_index cannot be free()'d.

ok. That is the situation we're in.

Show 8 quoted lines

>
> Add an exception for this in repo_clear(). In the future perhaps we
> would be able to allocate the_repository's index on heap too. Then we
> can remove revert this.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  I was trying to test the new parsed_object_pool_clear() and found this.

So this would go with the latest sb/object-store-alloc ?

My impression was that we never call repo_clear() on the_repository, which would allow us to special case the_repository further just as I did in v2 of that series[1] by having static allocations for certain objects in case of \ the_repository.

[1] https://public-inbox.org/git/20180501213403.14643-14-sbeller@google.com/

We could just deal with all the exceptions, but that makes repo_clear ugly IMHO.

I would rather special case the_repository even more instead of having it allocate all its things on the heap. (However we rather want to profile it and argue with data....)

Show 15 quoted lines

>  repository.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/repository.c b/repository.c
> index a4848c1bd0..f44733524a 100644
> --- a/repository.c
> +++ b/repository.c
> @@ -238,7 +238,9 @@ void repo_clear(struct repository *repo)
>
>         if (repo->index) {
>                 discard_index(repo->index);
> -               FREE_AND_NULL(repo->index);
> +               if (repo->index != &the_index)
> +                       free(repo->index);
> +               repo->index = NULL;

So after this we have a "dangling" the_index. It is not really dangling, but it is not part of the_repository any more and many places still use the_index, it might make up for interesting bugs?

What is your use case of repo_clear(the_repository)?

Thanks, Stefan