linux-kernel - Re: [PATCH v8 1/6] fs/posix_acl: Update the comments and support lightweight cache skipping

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Message-ID: <CAOssrKf0cuxx1YLiwFJHSnzMOOoejjWWibs98Mb5KSXVSSXfOg@mail.gmail.com>
Date:   Mon, 5 Mar 2018 10:53:41 +0100
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alban Crequy <alban@...volk.io>,
        Seth Forshee <seth.forshee@...onical.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Dongsu Park <dongsu@...volk.io>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v8 1/6] fs/posix_acl: Update the comments and support
 lightweight cache skipping

On Fri, Mar 2, 2018 at 10:59 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> The code has been missing a way for a ->get_acl method to not cache
> a return value without risking invalidating a cached value
> that was set while get_acl() was returning.
>
> Add that support by implementing to_uncachable_acl, to_cachable_acl,
> is_uncacheable_acl, and dealing with uncachable acls in get_acl().

I don't like the pointer magic here.  Can't the uncachable bit just be
added to struct posix_acl?

 AFAICS that can be done even without increasing the size of that
struct (e.g. by unioning it with the rcu_head).

Thanks,
Miklos