linux-kernel - Re: [PATCH overlayfs-next v3 0/4] overlayfs: Optimize override/revert creds

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Message-ID: <CAOQ4uxiaRE_cQ9m9LZMEiDCeSQKkZDfsJbpt85ds6hgvjnwHUQ@mail.gmail.com>
Date: Tue, 5 Nov 2024 21:47:20 +0100
From: Amir Goldstein <amir73il@...il.com>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc: brauner@...nel.org, hu1.chen@...el.com, miklos@...redi.hu, 
	malini.bhandaru@...el.com, tim.c.chen@...el.com, mikko.ylinen@...el.com, 
	linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH overlayfs-next v3 0/4] overlayfs: Optimize override/revert creds

On Tue, Nov 5, 2024 at 8:35 PM Vinicius Costa Gomes
<vinicius.gomes@...el.com> wrote:
>
> Hi,
>
> This series is rebased on top of Amir's overlayfs-next branch.
>
> Changes from v2:
>  - Removed the "convert to guard()/scoped_guard()" patches (Miklos Szeredi);
>  - In the overlayfs code, convert all users of override_creds()/revert_creds() to the _light() versions by:
>       1. making ovl_override_creds() use override_creds_light();
>       2. introduce ovl_revert_creds() which calls revert_creds_light();
>       3. convert revert_creds() to ovl_revert_creds()
>    (Amir Goldstein);
>  - Fix an potential reference counting issue, as the lifetime
>    expectations of the mounter credentials are different (Christian
>    Brauner);
>

Hi Vicius,

The end result looks good to me, but we still need to do the series a
bit differently.

> The series is now much simpler:
>
> Patch 1: Introduce the _light() version of the override/revert cred operations;
> Patch 2: Convert backing-file.c to use those;
> Patch 3: Do the conversion to use the _light() version internally;

This patch mixes a small logic change and a large mechanical change
that is not a good mix.

I took the liberty to split out the large mechanical change to
ovl: use wrapper ovl_revert_creds()
and pushed it to branch
https://github.com/amir73il/linux/commits/ovl_creds

I then rebased overlayfs-next over this commit and resolved the
conflicts with the pure mechanical change.

Now you can rebase your patches over ovl_creds and they should
not be conflicting with overlayfs-next changes.

The reason I wanted to do this is that Christian could take your changes
as well as my ovl_creds branch through the vfs tree if he chooses to do so.

> Patch 4: Fix a potential refcounting issue

This patch cannot be separated from patch #3 because it would introduce the
refcount leak mid series.

But after I took out all the mechanical changes out of patch #3,
there should be no problem for you to squash patches #3 and #4 together.

One more nit: please use "ovl: ..." for commit titles instead of
"fs/overlayfs: ...".

Thanks,
Amir.