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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 510F8C4320E for ; Tue, 27 Jul 2021 21:01:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3BAC460F6E for ; Tue, 27 Jul 2021 21:01:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235024AbhG0VBg (ORCPT ); Tue, 27 Jul 2021 17:01:36 -0400 Received: from so254-9.mailgun.net ([198.61.254.9]:63647 "EHLO so254-9.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234451AbhG0VAc (ORCPT ); Tue, 27 Jul 2021 17:00:32 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1627419631; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=Kq1881QGwVFiiS4S0da3eS/MhMFX22cv5dovHiGH+eE=; b=RixwWH2T2kBRdxwdHdFYkFVsiFA6bzHcBGj7xMlgO7IIDBQEUVUmD/DCQxllJJDIY5PWVTvs zO1JHkloBHHEKBSepO7VI3tEFyqHggO50aD7w3o/N4IsZCpASoHYsvRcGytT8165R2IsVikT q/5grSbAZG+eTryIlDpb7JGeh88= 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-east-1.postgun.com with SMTP id 610073e417c2b4047d539d4b (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 27 Jul 2021 21:00:20 GMT Sender: wcheng=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id A45A0C43152; Tue, 27 Jul 2021 21:00:19 +0000 (UTC) Received: from [10.110.37.24] (i-global254.qualcomm.com [199.106.103.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: wcheng) by smtp.codeaurora.org (Postfix) with ESMTPSA id 1DC5CC43148; Tue, 27 Jul 2021 21:00:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 1DC5CC43148 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=wcheng@codeaurora.org Subject: Re: [PATCH v2] usb: dwc3: gadget: Replace list_for_each_entry_safe() if using giveback To: Felipe Balbi , gregkh@linuxfoundation.org, peter.chen@kernel.org Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, jackp@codeaurora.org References: <1620716636-12422-1-git-send-email-wcheng@codeaurora.org> <87tun9g01v.fsf@kernel.org> <2675db9e-0cab-06b5-2986-0b4456a1f040@codeaurora.org> <5156238d-c1d8-a0d3-47af-8b52467fd071@codeaurora.org> <87v954xjoz.fsf@kernel.org> From: Wesley Cheng Message-ID: <3c55dd4f-5ebd-3730-7428-cb15235465a7@codeaurora.org> Date: Tue, 27 Jul 2021 14:00:16 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <87v954xjoz.fsf@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Hi Felipe, On 7/20/2021 11:30 PM, Felipe Balbi wrote: > > Hi Wesley, > > (first of all, sorry for the super long delay. This really fell through > the cracks) > No problem, I understand that you probably get a whole bunch of things all at once, so its hard to keep track of each one :). > Wesley Cheng writes: >> Hi Felipe, >> >> On 6/9/2021 1:57 PM, Wesley Cheng wrote: >>> Hi Felipe, >>> >>> On 5/19/2021 1:52 AM, Wesley Cheng wrote: >>>> >>>> >>>> On 5/11/2021 1:13 AM, Felipe Balbi wrote: >>>>> >>>>> Hi, >>>>> >>>>> Wesley Cheng writes: >>>>>> The list_for_each_entry_safe() macro saves the current item (n) and >>>>>> the item after (n+1), so that n can be safely removed without >>>>>> corrupting the list. However, when traversing the list and removing >>>>>> items using gadget giveback, the DWC3 lock is briefly released, >>>>>> allowing other routines to execute. There is a situation where, while >>>>>> items are being removed from the cancelled_list using >>>>>> dwc3_gadget_ep_cleanup_cancelled_requests(), the pullup disable >>>>>> routine is running in parallel (due to UDC unbind). As the cleanup >>>>>> routine removes n, and the pullup disable removes n+1, once the >>>>>> cleanup retakes the DWC3 lock, it references a request who was already >>>>>> removed/handled. With list debug enabled, this leads to a panic. >>>>>> Ensure all instances of the macro are replaced where gadget giveback >>>>>> is used. >>>>>> >>>>>> Example call stack: >>>>>> >>>>>> Thread#1: >>>>>> __dwc3_gadget_ep_set_halt() - CLEAR HALT >>>>>> -> dwc3_gadget_ep_cleanup_cancelled_requests() >>>>>> ->list_for_each_entry_safe() >>>>>> ->dwc3_gadget_giveback(n) >>>>>> ->dwc3_gadget_del_and_unmap_request()- n deleted[cancelled_list] >>>>>> ->spin_unlock >>>>>> ->Thread#2 executes >>>>>> ... >>>>>> ->dwc3_gadget_giveback(n+1) >>>>>> ->Already removed! >>>>>> >>>>>> Thread#2: >>>>>> dwc3_gadget_pullup() >>>>>> ->waiting for dwc3 spin_lock >>>>>> ... >>>>>> ->Thread#1 released lock >>>>>> ->dwc3_stop_active_transfers() >>>>>> ->dwc3_remove_requests() >>>>>> ->fetches n+1 item from cancelled_list (n removed by Thread#1) >>>>>> ->dwc3_gadget_giveback() >>>>>> ->dwc3_gadget_del_and_unmap_request()- n+1 deleted[cancelled_list] >>>>>> ->spin_unlock >>>>>> >>>>>> Fixes: d4f1afe5e896 ("usb: dwc3: gadget: move requests to cancelled_list") >>>>>> Signed-off-by: Wesley Cheng >>>>>> Reviewed-by: Peter Chen >>>>>> --- >>>>>> Changes in v2: >>>>>> - Updated commit message with context call stack of an example scenario >>>>>> seen on device. >>>>>> >>>>>> drivers/usb/dwc3/gadget.c | 8 ++++---- >>>>>> 1 file changed, 4 insertions(+), 4 deletions(-) >>>>>> >>>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c >>>>>> index dd80e5c..efa939b 100644 >>>>>> --- a/drivers/usb/dwc3/gadget.c >>>>>> +++ b/drivers/usb/dwc3/gadget.c >>>>>> @@ -1737,10 +1737,10 @@ static void dwc3_gadget_ep_skip_trbs(struct dwc3_ep *dep, struct dwc3_request *r >>>>>> static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep) >>>>>> { >>>>>> struct dwc3_request *req; >>>>>> - struct dwc3_request *tmp; >>>>>> struct dwc3 *dwc = dep->dwc; >>>>>> >>>>>> - list_for_each_entry_safe(req, tmp, &dep->cancelled_list, list) { >>>>>> + while (!list_empty(&dep->cancelled_list)) { >>>>>> + req = next_request(&dep->cancelled_list); >>>>> >>>>> couldn't this be solved list_replace_init() instead? Then we can keep >>>>> using the regular list_for_each_entry_safe() which has an added semantic >>>>> meaning due to its name. >>>>> >>>> >>>> Hi Felipe, >>>> >>>> Sorry for the late response. So I tried with a list_replace_init() to >>>> within the list_for_each_entry_safe() loop to update tmp w/ the >>>> cancelled_list list head, but the issue was still observed. This is >>>> because we can't replace the reference the loop already has stored in >>>> tmp, which is simply updated as the current item on the next iteration. >>>> >>>> I believe this is what you were trying to achieve? >>>> >>> Was wondering if you had any further inputs on this change? As >>> mentioned, I tried a few things with list_replace_init(), which did not >>> work. >>> >> >> Sorry for the ping. Is this change OK to add as is? We've been running >> into this instance pretty frequently during our testing, so just wanted >> to close on the proper changes being merged upstream. > > The idea is this: > > struct list_head local; > > spin_lock_irq(&lock); > list_replace_init(&dwc->cancelled_list, &local); > spin_unlock_irq(&lock); > > list_for_each_entry_safe(req, tmp, &local, list) { > /* ... */ > } > > It looks to me this should work fine, no? You can also follow what > drivers/usb/core/hcd.c is doing in usb_giveback_urb_bh() and restarting > if dwc->cancelled_list is not empty after list_for_each_entry_safe(). > > Can you give that one a shot? > Great, thanks for this suggestion! Now I understand what you were referring to. I gave this a try and it works well. Will prepare a change to replace both places with list_replace_init() Thanks Wesley Cheng -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project