From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S965000AbcKOHuN (ORCPT <rfc822;w@1wt.eu>);
        Tue, 15 Nov 2016 02:50:13 -0500
Received: from bombadil.infradead.org ([198.137.202.9]:43019 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S933642AbcKOHuK (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 15 Nov 2016 02:50:10 -0500
Date: Tue, 15 Nov 2016 08:50:07 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
        Will Deacon <will.deacon@arm.com>,
        "Reshetova, Elena" <elena.reshetova@intel.com>,
        Arnd Bergmann <arnd@arndb.de>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        David Windsor <dave@progbits.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH 5/7] kref: Implement kref_put_lock()
Message-ID: <20161115075007.GM3142@twins.programming.kicks-ass.net>
References: <20161114173946.501528675@infradead.org>
 <20161114174446.690415221@infradead.org>
 <CAGXu5j++hLfOucZB__hxoYYhCTo_+a+PPYMLEtBwW=uYKiCwUw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAGXu5j++hLfOucZB__hxoYYhCTo_+a+PPYMLEtBwW=uYKiCwUw@mail.gmail.com>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Nov 14, 2016 at 12:35:48PM -0800, Kees Cook wrote:
> On Mon, Nov 14, 2016 at 9:39 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > Because home-rolling your own is _awesome_, stop doing it. Provide
> > kref_put_lock(), just like kref_put_mutex() but for a spinlock.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> >  include/linux/kref.h |   21 +++++++++++++++------
> >  net/sunrpc/svcauth.c |   15 ++++++++++-----
> >  2 files changed, 25 insertions(+), 11 deletions(-)
> >
> > --- a/include/linux/kref.h
> > +++ b/include/linux/kref.h
> > @@ -86,12 +86,21 @@ static inline int kref_put_mutex(struct
> >                                  struct mutex *lock)
> >  {
> >         WARN_ON(release == NULL);
> 
> This WARN_ON makes sense, yes, though it seems like it should be deal
> with differently. If it's NULL, we'll just Oops when we call release()
> later... Seems like this should saturate the kref or something else
> similar.

So I simply took the pattern from the existing kref_put().

But I like it more in these kref_put_{lock,mutex}() variants, because
someone will need to unlock. If we simply crash/bug without unlock we'll
have broken state the rest of the kernel cannot fix up.