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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 D3AE8C48BC2 for ; Mon, 21 Jun 2021 13:53:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB31861206 for ; Mon, 21 Jun 2021 13:53:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230059AbhFUNzs (ORCPT ); Mon, 21 Jun 2021 09:55:48 -0400 Received: from netrider.rowland.org ([192.131.102.5]:50323 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S229747AbhFUNzr (ORCPT ); Mon, 21 Jun 2021 09:55:47 -0400 Received: (qmail 414341 invoked by uid 1000); 21 Jun 2021 09:53:32 -0400 Date: Mon, 21 Jun 2021 09:53:32 -0400 From: Alan Stern To: linyyuan@codeaurora.org Cc: Felipe Balbi , Thinh Nguyen , Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Jack Pham Subject: Re: [PATCH v3 1/2] usb: udc: core: hide struct usb_gadget_driver to gadget driver Message-ID: <20210621135332.GA413023@rowland.harvard.edu> References: <20210619154309.52127-1-linyyuan@codeaurora.org> <20210619154309.52127-2-linyyuan@codeaurora.org> <20210620021337.GA361976@rowland.harvard.edu> <42b3ebc2316495328e2d0061af81ef17@codeaurora.org> <018a4e222c2c3d6f5ca63b5f2036f8d8@codeaurora.org> <20210620134743.GA377492@rowland.harvard.edu> <98c2729c25442d6c66131d17cabdda27@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <98c2729c25442d6c66131d17cabdda27@codeaurora.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 21, 2021 at 09:37:34AM +0800, linyyuan@codeaurora.org wrote: > On 2021-06-20 21:47, Alan Stern wrote: > > On Sun, Jun 20, 2021 at 11:53:18AM +0800, linyyuan@codeaurora.org wrote: > > > On 2021-06-20 11:46, linyyuan@codeaurora.org wrote: > > > > On 2021-06-20 10:13, Alan Stern wrote: > > > > > On Sat, Jun 19, 2021 at 11:43:08PM +0800, Linyu Yuan wrote: > > > > > > currently most gadget driver have a pointer to save > > > > > > struct usb_gadget_driver from upper layer, > > > > > > it allow upper layer set and unset of the pointer. > > > > > > > > > > > > there is race that upper layer unset the pointer first, > > > > > > but gadget driver use the pointer later, > > > > > > and it cause system crash due to NULL pointer access. > > > > > > > > > > This race has already been fixed in Greg's usb-next branch. See > > > > > commit > > > > > 7dc0c55e9f30 ("USB: UDC core: Add udc_async_callbacks gadget op") and > > > > > following commits 04145a03db9d ("USB: UDC: Implement > > > > > udc_async_callbacks in dummy-hcd") and b42e8090ba93 ("USB: UDC: > > > > > Implement udc_async_callbacks in net2280"). > > > > > > > > > thanks, this is better, lower driver only need change several places. > > > > > You just need to write a corresponding patch implementing the > > > > > async_callbacks op for dwc3. > > > > yes, i will do. > > > > > > > > Alan, i want to discuss your suggestion again in b42e8090ba93 ("USB: > > > UDC: > > > Implement udc_async_callbacks in net2280") > > > > > > + if (dev->async_callbacks) { ----> if CPU1 > > > saw this > > > is true > > > + spin_unlock(&dev->lock); ---> CPU2 > > > get lock > > > after this unlock, > > > it will set async_callbacks to false, then follow call also crash, > > > right ? > > > + tmp = dev->driver->setup(&dev->gadget, > > > &u.r); > > > + spin_lock(&dev->lock); > > > + } > > > > No, this is okay. The reason is because usb_gadget_remove_driver (CPU2 > > in your example) does this: > > > > usb_gadget_disable_async_callbacks(udc); > > if (udc->gadget->irq) > > synchronize_irq(udc->gadget->irq); > > udc->driver->unbind(udc->gadget); > > usb_gadget_udc_stop(udc); > > > > The synchronize_irq call will make CPU2 wait until CPU1 has finished > > handling the interrupt for the setup packet. The system won't crash, > > because dev->driver->setup will be called before unbind and udc_stop > > instead of after. > still several question, > 1. how about suspend calll dev->driver->suspend ? The same reasoning applies. The synchronize_irq call will make CPU2 wait until CPU1 has finished handling the interrupt for the USB bus suspend. The system won't crash, because dev->driver->suspend will be called before unbind and udc_stop instead of after. > 2. will 04145a03db9d ("USB: UDC: Implement udc_async_callbacks in > dummy-hcd") backport to LTS branch ? None of these commits are marked for back-porting to the -stable kernels. The race they fix does not occur often. If you the commits to be applied to the LTS stable kernels, you can ask Greg KH to do it. > 3. how about coding style ? so following code > if (foo->gadget_driver && foo->gadget_driver->resume) > change to > if (foo->asnyc_callbacks && foo->gadget_driver->resume) I don't understand this question. Alan Stern