From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BBC9C433E0 for ; Mon, 29 Mar 2021 18:50:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DDB6361613 for ; Mon, 29 Mar 2021 18:50:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231404AbhC2SuG (ORCPT ); Mon, 29 Mar 2021 14:50:06 -0400 Received: from netrider.rowland.org ([192.131.102.5]:35611 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S230224AbhC2Str (ORCPT ); Mon, 29 Mar 2021 14:49:47 -0400 Received: (qmail 945935 invoked by uid 1000); 29 Mar 2021 14:49:46 -0400 Date: Mon, 29 Mar 2021 14:49:46 -0400 From: Alan Stern To: Heikki Krogerus Cc: Greg Kroah-Hartman , Benson Leung , Prashant Malani , Guenter Roeck , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 5/6] usb: Iterator for ports Message-ID: <20210329184946.GA944482@rowland.harvard.edu> References: <20210329084426.78138-1-heikki.krogerus@linux.intel.com> <20210329084426.78138-6-heikki.krogerus@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210329084426.78138-6-heikki.krogerus@linux.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 29, 2021 at 11:44:25AM +0300, Heikki Krogerus wrote: > Introducing usb_for_each_port(). It works the same way as > usb_for_each_dev(), but instead of going through every USB > device in the system, it walks through the USB ports in the > system. > > Signed-off-by: Heikki Krogerus > --- > drivers/usb/core/usb.c | 46 ++++++++++++++++++++++++++++++++++++++++++ > include/linux/usb.h | 1 + > 2 files changed, 47 insertions(+) > > diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c > index 2ce3667ec6fae..62368c4ed37af 100644 > --- a/drivers/usb/core/usb.c > +++ b/drivers/usb/core/usb.c > @@ -398,6 +398,52 @@ int usb_for_each_dev(void *data, int (*fn)(struct usb_device *, void *)) > } > EXPORT_SYMBOL_GPL(usb_for_each_dev); > > +struct each_hub_arg { > + void *data; > + int (*fn)(struct device *, void *); > +}; > + > +static int __each_hub(struct usb_device *hdev, void *data) > +{ > + struct each_hub_arg *arg = (struct each_hub_arg *)data; > + struct usb_hub *hub; > + int ret = 0; > + int i; > + > + hub = usb_hub_to_struct_hub(hdev); > + if (!hub) > + return 0; What happens if the hub is removed exactly now? Although hdev is reference-counted (and the loop iterator does take a reference to it), usb_hub_to_struct_hub doesn't take a reference to hub. And hub->ports isn't refcounted at all. > + > + mutex_lock(&usb_port_peer_mutex); > + > + for (i = 0; i < hdev->maxchild; i++) { > + ret = arg->fn(&hub->ports[i]->dev, arg->data); > + if (ret) > + break; > + } > + > + mutex_unlock(&usb_port_peer_mutex); I have a feeling that it would be better to take and release this mutex in usb_for_each_port (or its caller), so that it is held over the whole loop. Alan Stern > + > + return ret; > +} > + > +/** > + * usb_for_each_port - interate over all USB ports in the system > + * @data: data pointer that will be handed to the callback function > + * @fn: callback function to be called for each USB port > + * > + * Iterate over all USB ports and call @fn for each, passing it @data. If it > + * returns anything other than 0, we break the iteration prematurely and return > + * that value. > + */ > +int usb_for_each_port(void *data, int (*fn)(struct device *, void *)) > +{ > + struct each_hub_arg arg = {data, fn}; > + > + return usb_for_each_dev(&arg, __each_hub); > +} > +EXPORT_SYMBOL_GPL(usb_for_each_port); > + > /** > * usb_release_dev - free a usb device structure when all users of it are finished. > * @dev: device that's been disconnected > diff --git a/include/linux/usb.h b/include/linux/usb.h > index ddd2f5b2a2827..e4d2eb703cf89 100644 > --- a/include/linux/usb.h > +++ b/include/linux/usb.h > @@ -871,6 +871,7 @@ extern int usb_match_one_id(struct usb_interface *interface, > const struct usb_device_id *id); > > extern int usb_for_each_dev(void *data, int (*fn)(struct usb_device *, void *)); > +int usb_for_each_port(void *data, int (*fn)(struct device *, void *)); > extern struct usb_interface *usb_find_interface(struct usb_driver *drv, > int minor); > extern struct usb_interface *usb_ifnum_to_if(const struct usb_device *dev, > -- > 2.30.2 >