linux-kernel - Re: [PATCH] userns: suppress kmemleak message

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Date:   Thu, 15 Dec 2016 13:16:08 +0100
From:   Fubo Chen <fubo.chen@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jakub Kicinski <kubakici@...pl>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Berg <johannes@...solutions.net>,
        Maciej Żenczykowski <zenczykowski@...il.com>
Subject: Re: [PATCH] userns: suppress kmemleak message

On Thu, Nov 3, 2016 at 3:54 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Dmitry Torokhov <dmitry.torokhov@...il.com> writes:
>
>> We do not ever intend to unregister "user" sysctl table, unfortunately
>> it leads kmemleak to believe that we are leaking memory:
>
> Sounds like an issue with kmemleak because we do retain references.
>
> So no we don't intend to unregister the table.
>
> As for the patch.
>
> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>
> I can't see the using kmemleak_not_leak is possibly good form.  I
> would much rather have suggestions about constructs that won't confuse
> kmemleak and won't need ugly annotations that serve no purpose but to
> appease a tool.  Perhaps the user_header variable needs to be moved out
> of user_namespace_sysctl_init.

The only alternative I see is to use WRITE_ONCE() instead of "=" to
set "user_header" such that the compiler cannot optimize that variable
away. Which of these two approaches do you prefer?

Fubo.