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Date:   Fri, 3 Jan 2020 09:56:34 +0100
From:   Alexey Gladkov <gladkov.alexey@gmail.com>
To:     J Freyensee <why2jjj.linux@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Linux API <linux-api@vger.kernel.org>,
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        Akinobu Mita <akinobu.mita@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Daniel Micay <danielmicay@gmail.com>,
        Djalal Harouni <tixxdz@gmail.com>,
        "Dmitry V . Levin" <ldv@altlinux.org>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@poochiereds.net>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Solar Designer <solar@openwall.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [PATCH v6 07/10] proc: flush task dcache entries from all procfs
 instances
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References: <20191225125151.1950142-1-gladkov.alexey@gmail.com>
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 <8d85ba43-0759-358e-137d-246107bac747@gmail.com>
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On Mon, Dec 30, 2019 at 02:03:29PM -0800, J Freyensee wrote:
> > +#ifdef CONFIG_PROC_FS
> > +static inline void pidns_proc_lock(struct pid_namespace *pid_ns)
> > +{
> > +	down_write(&pid_ns->rw_proc_mounts);
> > +}
> > +
> > +static inline void pidns_proc_unlock(struct pid_namespace *pid_ns)
> > +{
> > +	up_write(&pid_ns->rw_proc_mounts);
> > +}
> > +
> > +static inline void pidns_proc_lock_shared(struct pid_namespace *pid_ns)
> > +{
> > +	down_read(&pid_ns->rw_proc_mounts);
> > +}
> > +
> > +static inline void pidns_proc_unlock_shared(struct pid_namespace *pid_ns)
> > +{
> > +	up_read(&pid_ns->rw_proc_mounts);
> > +}
> > +#else /* !CONFIG_PROC_FS */
> > +
> Apologies for my newbie question. I couldn't help but notice all these
> function calls are assuming that the parameter struct pid_namespace *pid_ns
> will never be NULL.? Is that a good assumption?

These inline helpers are introduced to improve readability. They only make
sense inside procfs. I don't think that defensive programming is useful
here.

-- 
Rgrds, legion