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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 D6718C388F7 for ; Tue, 10 Nov 2020 08:39:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8CB4D20870 for ; Tue, 10 Nov 2020 08:39:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="G9nkPdrW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730719AbgKJIj6 (ORCPT ); Tue, 10 Nov 2020 03:39:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:33978 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730116AbgKJIj4 (ORCPT ); Tue, 10 Nov 2020 03:39:56 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DD8E020731; Tue, 10 Nov 2020 08:39:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604997595; bh=PXiAAftzN6GduD3leXdMMam7ZG0s3JyEEMG4p6SdMvc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=G9nkPdrWtPrJduPcSdxHmqQpUnc0aHS598O0eKE8RN4F3wOqBYdHhwl40XikGeC6u d2KyuQ1Zz6/EZ+07G7F9QskpEHC3YJ6CDjP97u8EJxstu+OmWTlwd4APq0fdlhSX1d zgFGvmXo6zRmpFOjP9gbPmwF6STfNC3h6RcPUu4g= Date: Tue, 10 Nov 2020 09:40:51 +0100 From: Greg KH To: thomas.haemmerle@wolfvision.net Cc: laurent.pinchart@ideasonboard.com, balbi@kernel.org, linux-usb@vger.kernel.org, m.tretter@pengutronix.de, linux-media@vger.kernel.org Subject: Re: [PATCH v2] usb: gadget: uvc: fix multiple opens Message-ID: References: <20201105103758.GA4033354@kroah.com> <20201110082504.26134-1-thomas.haemmerle@wolfvision.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201110082504.26134-1-thomas.haemmerle@wolfvision.net> Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Tue, Nov 10, 2020 at 09:25:04AM +0100, thomas.haemmerle@wolfvision.net wrote: > From: Thomas Haemmerle > > Currently, the UVC function is activated when open on the corresponding > v4l2 device is called. > On another open the activation of the function fails since the > deactivation counter in `usb_function_activate` equals 0. However the > error is not returned to userspace since the open of the v4l2 device is > successful. > > On a close the function is deactivated (since deactivation counter still > equals 0) and the video is disabled in `uvc_v4l2_release`, although > another process potentially is streaming. > > Move activation of UVC function to subscription on UVC_EVENT_SETUP and > keep track of the number of subscribers (limited to 1) because there we > can guarantee for a userspace program utilizing UVC. > Extend the `struct uvc_file_handle` with member `bool connected` to tag > it for a deactivation of the function. > > With this a process is able to check capabilities of the v4l2 device > without deactivating the function for another process actually using the > device for UVC streaming. > > Signed-off-by: Thomas Haemmerle > --- > v2: > - fix deadlock in `uvc_v4l2_unsubscribe_event()` (mutex is already > locked in v4l2-core) introduced in v1 > - lock mutex in `uvc_v4l2_release()` to suppress ioctls and protect > connected > > drivers/usb/gadget/function/uvc.h | 2 + > drivers/usb/gadget/function/uvc_v4l2.c | 56 +++++++++++++++++++++----- > 2 files changed, 48 insertions(+), 10 deletions(-) > > diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h > index 73da4f9a8d4c..0d0bcbffc8fd 100644 > --- a/drivers/usb/gadget/function/uvc.h > +++ b/drivers/usb/gadget/function/uvc.h > @@ -117,6 +117,7 @@ struct uvc_device { > enum uvc_state state; > struct usb_function func; > struct uvc_video video; > + unsigned int connections; > > /* Descriptors */ > struct { > @@ -147,6 +148,7 @@ static inline struct uvc_device *to_uvc(struct usb_function *f) > struct uvc_file_handle { > struct v4l2_fh vfh; > struct uvc_video *device; > + bool connected; What protects these two fields you are adding? > }; > > #define to_uvc_file_handle(handle) \ > diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c > index 67922b1355e6..aee4888e17b1 100644 > --- a/drivers/usb/gadget/function/uvc_v4l2.c > +++ b/drivers/usb/gadget/function/uvc_v4l2.c > @@ -228,17 +228,57 @@ static int > uvc_v4l2_subscribe_event(struct v4l2_fh *fh, > const struct v4l2_event_subscription *sub) > { > + struct uvc_device *uvc = video_get_drvdata(fh->vdev); > + struct uvc_file_handle *handle = to_uvc_file_handle(fh); > + int ret; > + > if (sub->type < UVC_EVENT_FIRST || sub->type > UVC_EVENT_LAST) > return -EINVAL; > > - return v4l2_event_subscribe(fh, sub, 2, NULL); > + if ((sub->type == UVC_EVENT_SETUP) && (uvc->connections >= 1)) > + return -EBUSY; Are you sure you can't handle more than one connection? If so, why is it an integer and not just a boolean? And what prevents the value from changing right after you test it here? > + > + ret = v4l2_event_subscribe(fh, sub, 2, NULL); > + if (ret < 0) > + return ret; > + > + if (sub->type == UVC_EVENT_SETUP) { > + uvc->connections++; > + handle->connected = true; > + uvc_function_connect(uvc); > + } > + > + return 0; > +} > + > +static void uvc_v4l2_disable(struct uvc_device *uvc) > +{ > + if (--uvc->connections) > + return; > + What prevents "connections" from changing right after testing it here? thanks, greg k-h