From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758523Ab3EWOUn (ORCPT ); Thu, 23 May 2013 10:20:43 -0400 Received: from smtp-out-100.synserver.de ([212.40.185.100]:1051 "EHLO smtp-out-100.synserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754876Ab3EWOUm (ORCPT ); Thu, 23 May 2013 10:20:42 -0400 X-SynServer-TrustedSrc: 1 X-SynServer-AuthUser: lars@metafoo.de X-SynServer-PPID: 13974 Message-ID: <519E25AB.4060406@metafoo.de> Date: Thu, 23 May 2013 16:20:27 +0200 From: Lars-Peter Clausen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130116 Icedove/10.0.12 MIME-Version: 1.0 To: Mark Brown CC: Davide Ciminaghi , Stephen Warren , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] regmap: Make regmap-mmio usable from different contexts References: <1369314377-22873-1-git-send-email-lars@metafoo.de> <1369314377-22873-2-git-send-email-lars@metafoo.de> <20130523140503.GD2412@sirena.org.uk> In-Reply-To: <20130523140503.GD2412@sirena.org.uk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/23/2013 04:05 PM, Mark Brown wrote: > On Thu, May 23, 2013 at 03:06:16PM +0200, Lars-Peter Clausen wrote: > >> This patch updates the adds a flags parameter to the regmap lock and unlock >> callbacks and uses spin_lock_irqsave() and spin_unlock_restore() for the mmio >> case. This allows us to use regmap-mmio from different contexts. > > This seems really invasive, why not just have the lock that gets passed > in point to a struct which has both the lock and the flags? As far as > the core is concerned the lock is just whatever data is required to do > the locking, the fact that it's actually two values is an implementation > detail of this locking implementation. I think that won't work. spin_lock_irqsave() will write to the flags parameter before it has successfully taken the look. So if a process running on another CPU tries to acquire the the lock while it is already held we'll end up overwriting the flags. E.g: CPU0 CPU1 spin_lock_irqsave() - write flags spin_lock_irqsave() - overwrite flags spin_unlock_irqrestore() - restore wrong flags Hence flags needs to go onto the stack. - Lars