linux-kernel - Re: [PATCH] cred: Use RCU primitives to access RCU pointers

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Message-ID: <267885.1580492989@warthog.procyon.org.uk>
Date:   Fri, 31 Jan 2020 17:49:49 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     dhowells@...hat.com, Amol Grover <frextrite@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] cred: Use RCU primitives to access RCU pointers

Jann Horn <jannh@...gle.com> wrote:

> > task_struct.cred and task_struct.real_cred are annotated by __rcu,
> 
> task_struct.cred doesn't actually have RCU semantics though, see
> commit d7852fbd0f0423937fa287a598bfde188bb68c22. For task_struct.cred,
> it would probably be more correct to remove the __rcu annotation?

You're right, I think, there shouldn't be any need for __rcu on
task_struct::cred since it shouldn't be accessed on any task except current.

I've a feeling that there was something at the time, proc perhaps, but I don't
remember.

David