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=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 4FDA5C49EA7 for ; Sun, 27 Jun 2021 02:49:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3087161C55 for ; Sun, 27 Jun 2021 02:49:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230424AbhF0CvX (ORCPT ); Sat, 26 Jun 2021 22:51:23 -0400 Received: from so254-9.mailgun.net ([198.61.254.9]:50020 "EHLO so254-9.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230214AbhF0CvX (ORCPT ); Sat, 26 Jun 2021 22:51:23 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1624762140; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=MRStp5Lf5S4mzb1+rC3cp0h9PtU2m4YOTYmUov94j2Y=; b=XrXoVaty5X4d0StJXJYqoyeJAGNzCV4xdqaylN2webhMH1crCuojcKkMg+3ZhtYGHVjGtrmH nvHmafxl5PsGQD7ZsHqjF1cDtjnDvq4pFnjbpT7kQZ8x29tamAmbnH1jVWc1NSFNU8XuY5/D efXM7lxRXK2168lcUlbj5cYYfVg= X-Mailgun-Sending-Ip: 198.61.254.9 X-Mailgun-Sid: WyIxZTE2YSIsICJsaW51eC11c2JAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n07.prod.us-west-2.postgun.com with SMTP id 60d7e7192a2a9a9761c77f51 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Sun, 27 Jun 2021 02:48:57 GMT Sender: linyyuan=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id B249FC43460; Sun, 27 Jun 2021 02:48:57 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: linyyuan) by smtp.codeaurora.org (Postfix) with ESMTPSA id CED2BC433F1; Sun, 27 Jun 2021 02:48:56 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Sun, 27 Jun 2021 10:48:56 +0800 From: linyyuan@codeaurora.org To: Alan Stern Cc: Felipe Balbi , Thinh Nguyen , Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Jack Pham Subject: Re: [PATCH] usb: dwc3: fix race of usb_gadget_driver operation In-Reply-To: <20210626150304.GA601624@rowland.harvard.edu> References: <20210625104415.8072-1-linyyuan@codeaurora.org> <20210625163707.GC574023@rowland.harvard.edu> <20210626150304.GA601624@rowland.harvard.edu> Message-ID: <1d1f06763c7cdeb67264128537c6a8f4@codeaurora.org> X-Sender: linyyuan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On 2021-06-26 23:03, Alan Stern wrote: > On Sat, Jun 26, 2021 at 09:16:25AM +0800, linyyuan@codeaurora.org > wrote: >> On 2021-06-26 00:37, Alan Stern wrote: >> > On Fri, Jun 25, 2021 at 06:44:15PM +0800, Linyu Yuan wrote: > >> > > --- a/drivers/usb/dwc3/ep0.c >> > > +++ b/drivers/usb/dwc3/ep0.c >> > > @@ -597,10 +597,11 @@ static int dwc3_ep0_set_address(struct dwc3 >> > > *dwc, struct usb_ctrlrequest *ctrl) >> > > >> > > static int dwc3_ep0_delegate_req(struct dwc3 *dwc, struct >> > > usb_ctrlrequest *ctrl) >> > > { >> > > - int ret; >> > > + int ret = 0; >> > > >> > > spin_unlock(&dwc->lock); >> > > - ret = dwc->gadget_driver->setup(dwc->gadget, ctrl); >> > > + if (dwc->async_callbacks) >> > > + ret = dwc->gadget_driver->setup(dwc->gadget, ctrl); >> > > spin_lock(&dwc->lock); >> > >> > Here and in the other places, you should test dwc->async_callbacks >> > _before_ dropping the spinlock. Otherwise there is a race (the flag >> > could be written at about the same time it is checked). >> thanks for your comments, >> >> if you think there is race here, how to make sure gadget_driver >> pointer is >> safe, >> this is closest place where we can confirm it is non-NULL by checking >> async_callbacks ? > > I explained this twice already: We know that gadget_driver is not > NULL because usb_gadget_remove_driver calls synchronize_irq before > doing usb_gadget_udc_stop. > > Look at this timing diagram: > > CPU0 CPU1 > ---- ---- > IRQ happens for setup packet > Handler sees async_callbacks > is enabled > Handler unlocks dwc->lock > usb_gadget_remove_driver runs > Disables async callbacks > Calls synchronize_irq > Handler calls dwc-> . waits for IRQ handler to > gadget_driver->setup . return > Handler locks dwc-lock . > ... . > Handler returns . > . synchronize_irq returns > Calls usb_gadget_udc_stop > dwc->gadget_driver is > set to NULL > > As you can see, dwc->gadget_driver is non-NULL when CPU0 uses it, > even though async_callbacks gets cleared during the time when the > lock is released. thanks for your patient explanation, but from this part, seem it is synchronize_irq() help to avoid NULL pointer crash. can you also explain how async_callbacks flag help here ? > > Alan Stern