From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752329Ab1LLKSx (ORCPT ); Mon, 12 Dec 2011 05:18:53 -0500 Received: from cantor2.suse.de ([195.135.220.15]:38215 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751323Ab1LLKSu (ORCPT ); Mon, 12 Dec 2011 05:18:50 -0500 From: Oliver Neukum Organization: SUSE To: Ming Lei Subject: Re: [PATCH 3/3] kref: Remove the memory barriers Date: Mon, 12 Dec 2011 11:20:16 +0100 User-Agent: KMail/1.13.5 (Linux/3.2.0-rc4-12-desktop+; KDE/4.4.4; x86_64; ; ) Cc: Peter Zijlstra , gregkh@suse.de, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, ostrikov@nvidia.com, adobriyan@gmail.com, eric.dumazet@gmail.com, mingo@elte.hu References: <20111210104341.592561407@chello.nl> <1323680078.16764.45.camel@twins> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201112121120.16326.oneukum@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am Montag, 12. Dezember 2011, 10:57:31 schrieb Ming Lei: > On Mon, Dec 12, 2011 at 4:54 PM, Peter Zijlstra wrote: > > On Mon, 2011-12-12 at 11:48 +0800, Ming Lei wrote: > >> For kref, maybe it is still multiple operations done on one cpu vs them > >> being visible on another, but seems a bit implicit, see the common kref > >> usage below: > >> > >> CPU0 CPU1 > >> A:kref_init(&obj->ref) > > > > how does CPU0 get a ref to obj? > > Suppose open/close/read/.. context is run on CPU0, and driver .probe/.release > context(hotplug context) is run on CPU1. There are a few examples on > usb driver(eg. usb-skeleton.c, ...) USB generally relies on an implied barrier just as: /* we can register the device now, as it is ready */ retval = usb_register_dev(interface, &skel_class); Generally reference counting cannot help you if kfree() is involved Regards Oliver