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 S1752928AbbGKGWg (ORCPT <rfc822;w@1wt.eu>);
	Sat, 11 Jul 2015 02:22:36 -0400
Received: from mail.linuxfoundation.org ([140.211.169.12]:39815 "EHLO
	mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752069AbbGKGWf (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 11 Jul 2015 02:22:35 -0400
Date: Fri, 10 Jul 2015 18:33:57 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Minchan Kim <minchan@kernel.org>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] mm/shrinker: define INIT_SHRINKER macro
Message-Id: <20150710183357.30605207.akpm@linux-foundation.org>
In-Reply-To: <20150711012513.GB811@swordfish>
References: <20150710011211.GB584@swordfish>
	<20150710153235.835c4992fbce526da23361d0@linux-foundation.org>
	<20150711012513.GB811@swordfish>
X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sat, 11 Jul 2015 10:25:13 +0900 Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:

> > > I was thinking of a trivial INIT_SHRINKER macro to init `struct shrinker'
> > > internal members (composed in email client, not tested)
> > > 
> > > include/linux/shrinker.h
> > > 
> > > #define INIT_SHRINKER(s)			\
> > > 	do {					\
> > > 		(s)->nr_deferred = NULL;	\
> > > 		INIT_LIST_HEAD(&(s)->list);	\
> > > 	} while (0)
> > 
> > Spose so.  Although it would be simpler to change unregister_shrinker()
> > to bale out if list.next==NULL and then say "all zeroes is the
> > initialized state".
> 
> Yes, or '->nr_deferred == NULL' -- we can't have NULL ->nr_deferred
> in a properly registered shrinker (as of now)

list.next seems safer because that will always be non-zero.  But
whatever - we can change it later.
 
> But that will not work if someone has accidentally passed not zeroed
> out pointer to unregister.

I wouldn't worry about that really.  If you pass a pointer to
uninitialized memory, the kernel will explode.  That's true of just
about every pointer-accepting function in the kernel.