From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755392AbcIKUn0 (ORCPT ); Sun, 11 Sep 2016 16:43:26 -0400 Received: from mailout1.hostsharing.net ([83.223.95.204]:50685 "EHLO mailout1.hostsharing.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753693AbcIKUnY (ORCPT ); Sun, 11 Sep 2016 16:43:24 -0400 Date: Sun, 11 Sep 2016 22:43:36 +0200 From: Lukas Wunner To: "Rafael J. Wysocki" Cc: Linux PM list , Greg Kroah-Hartman , Alan Stern , Linux Kernel Mailing List , Tomeu Vizoso , Mark Brown , Marek Szyprowski , Kevin Hilman , Ulf Hansson , "Luis R. Rodriguez" Subject: Re: [RFC/RFT][PATCH v2 2/7] driver core: Functional dependencies tracking support Message-ID: <20160911204336.GA371@wunner.de> References: <27296716.H9VWo8ShOm@vostro.rjw.lan> <2169291.li0uc2Ryoq@vostro.rjw.lan> <20160911134058.GA189@wunner.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160911134058.GA189@wunner.de> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 11, 2016 at 03:40:58PM +0200, Lukas Wunner wrote: > On Thu, Sep 08, 2016 at 11:27:45PM +0200, Rafael J. Wysocki wrote: > > +/** > > + * device_is_dependent - Check if one device depends on another one > > + * @dev: Device to check dependencies for. > > + * @target: Device to check against. > > + * > > + * Check if @dev or any device dependent on it (its child or its consumer etc) > > + * depends on @target. Return 1 if that is the case or 0 otherwise. > > + */ > > +static int device_is_dependent(struct device *dev, void *target) > > +{ > > + struct device_link *link; > > + int ret; > > + > > + ret = device_for_each_child(dev, target, device_is_dependent); > > + list_for_each_entry(link, &dev->links_to_consumers, s_node) { > > + if (WARN_ON(link->consumer == target)) > > + return 1; > > + > > + ret = ret || device_is_dependent(link->consumer, target); > > + } > > + return ret; > > +} > > What happens if someone tries to add a device link from a parent > (as the consumer) to a child (as a supplier)? You're only checking > if target is a consumer of dev, for full correctness you'd also have > to check if target is a parent of dev. (Or grandparent, or great- > grandparent, ... you need to walk the tree up to the root.) > > > The function can be sped up by returning immediately if a match > is found instead of continuing searching and accumulating the > result in ret, i.e.: > > if (device_for_each_child(dev, target, device_is_dependent)) > return 1; > > and in the list_for_each_entry block: > > if (device_is_dependent(link->consumer, target)) > return 1; > > Then at the end of the function "return 0". > > > I'd move the WARN_ON() to the single invocation of this function in > device_link_add(), that way it's possible to use the function as a > helper elsewhere should the need arise. Oh I'm grasping only now, you want to emit a WARN for *every* infringing child/consumer. That could lead to a WARN flood if a developer accidentally does something really dumb, like linking the PCI root to some PCI endpoint device, but fair enough. The point about linking a parent to a child still stands however. I think a simple way to check this is to just add if (WARN_ON(dev == target)) return 1; at the top of the function, because when someone tries to link a parent to a child, when recursing from the parent downward one will eventually hit that child. This will also prevent someone from linking a device to itself. Best regards, Lukas