linux-kernel - Re: [RFC PATCH 0/3] Rework locking when rendering mountinfo cgroup paths

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Date:   Tue, 23 May 2023 14:09:12 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dave Chinner <dchinner@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Jiri Wiesner <jwiesner@...e.de>
Subject: Re: [RFC PATCH 0/3] Rework locking when rendering mountinfo cgroup
 paths

On Tue, May 02, 2023 at 03:38:44PM +0200, Michal Koutný wrote:
> Idea for these modification came up when css_set_lock seemed unneeded in
> cgroup_show_path.
> It's a delicate change, so the deciding factor was when cgroup_show_path popped
> up also in some profiles of frequent mountinfo readers.
> The idea is to trade the exclusive css_set_lock for the shared
> namespace_sem when rendering cgroup paths. Details are described more in

I have no issue with the cgroup specific part of relying on
namespace_sem but kernel/cgroup/ has no business of being aware of
namespace semaphore in any way. Leave a comment to clarify what you're
doing but we're not going to sprinkle namespace_sem references - even if
only for the sake of lockdep - into other subsystems.