From patchwork Sat Jul 29 14:59:38 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alan Stern X-Patchwork-Id: 708269 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8823EC001E0 for ; Sat, 29 Jul 2023 14:59:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229897AbjG2O7k (ORCPT ); Sat, 29 Jul 2023 10:59:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232047AbjG2O7k (ORCPT ); Sat, 29 Jul 2023 10:59:40 -0400 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by lindbergh.monkeyblade.net (Postfix) with SMTP id A856335B6 for ; Sat, 29 Jul 2023 07:59:38 -0700 (PDT) Received: (qmail 70073 invoked by uid 1000); 29 Jul 2023 10:59:38 -0400 Date: Sat, 29 Jul 2023 10:59:38 -0400 From: Alan Stern To: Greg KH Cc: Avichal Rakesh , Badhri Jagan Sridharan , USB mailing list Subject: [PATCH] USB: Gadget: core: Help prevent panic during UVC unconfigure Message-ID: <48b2f1f1-0639-46bf-bbfc-98cb05a24914@rowland.harvard.edu> MIME-Version: 1.0 Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Avichal Rakesh reported a kernel panic that occurred when the UVC gadget driver was removed from a gadget's configuration. The panic involves a somewhat complicated interaction between the kernel driver and a userspace component (as described in the Link tag below), but the analysis did make one thing clear: The Gadget core should accomodate gadget drivers calling usb_gadget_deactivate() as part of their unbind procedure. Currently this doesn't work. gadget_unbind_driver() calls driver->unbind() while holding the udc->connect_lock mutex, and usb_gadget_deactivate() attempts to acquire that mutex, which will result in a deadlock. The simple fix is for gadget_unbind_driver() to release the mutex when invoking the ->unbind() callback. There is no particular reason for it to be holding the mutex at that time, and the mutex isn't held while the ->bind() callback is invoked. So we'll drop the mutex before performing the unbind callback and reacquire it afterward. We'll also add a couple of comments to usb_gadget_activate() and usb_gadget_deactivate(). Because they run in process context they must not be called from a gadget driver's ->disconnect() callback, which (according to the kerneldoc for struct usb_gadget_driver in include/linux/usb/gadget.h) may run in interrupt context. This may help prevent similar bugs from arising in the future. Reported-and-tested-by: Avichal Rakesh Signed-off-by: Alan Stern Fixes: 286d9975a838 ("usb: gadget: udc: core: Prevent soft_connect_store() race") Link: https://lore.kernel.org/linux-usb/4d7aa3f4-22d9-9f5a-3d70-1bd7148ff4ba@google.com/ Cc: Badhri Jagan Sridharan Cc: --- drivers/usb/gadget/udc/core.c | 9 +++++++++ 1 file changed, 9 insertions(+) Index: usb-devel/drivers/usb/gadget/udc/core.c =================================================================== --- usb-devel.orig/drivers/usb/gadget/udc/core.c +++ usb-devel/drivers/usb/gadget/udc/core.c @@ -822,6 +822,9 @@ EXPORT_SYMBOL_GPL(usb_gadget_disconnect) * usb_gadget_activate() is called. For example, user mode components may * need to be activated before the system can talk to hosts. * + * This routine may sleep; it must not be called in interrupt context + * (such as from within a gadget driver's disconnect() callback). + * * Returns zero on success, else negative errno. */ int usb_gadget_deactivate(struct usb_gadget *gadget) @@ -860,6 +863,8 @@ EXPORT_SYMBOL_GPL(usb_gadget_deactivate) * This routine activates gadget which was previously deactivated with * usb_gadget_deactivate() call. It calls usb_gadget_connect() if needed. * + * This routine may sleep; it must not be called in interrupt context. + * * Returns zero on success, else negative errno. */ int usb_gadget_activate(struct usb_gadget *gadget) @@ -1639,7 +1644,11 @@ static void gadget_unbind_driver(struct usb_gadget_disable_async_callbacks(udc); if (gadget->irq) synchronize_irq(gadget->irq); + mutex_unlock(&udc->connect_lock); + udc->driver->unbind(gadget); + + mutex_lock(&udc->connect_lock); usb_gadget_udc_stop_locked(udc); mutex_unlock(&udc->connect_lock);