linux-kernel - Re: [PATCH v6 07/10] proc: flush task dcache entries from all procfs instances

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Date:   Fri, 3 Jan 2020 09:56:34 +0100
From:   Alexey Gladkov <gladkov.alexey@...il.com>
To:     J Freyensee <why2jjj.linux@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Security Module <linux-security-module@...r.kernel.org>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Solar Designer <solar@...nwall.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v6 07/10] proc: flush task dcache entries from all procfs
 instances

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