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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 063D4C4167B for ; Wed, 6 Dec 2023 02:25:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229617AbjLFCZX (ORCPT ); Tue, 5 Dec 2023 21:25:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229493AbjLFCZW (ORCPT ); Tue, 5 Dec 2023 21:25:22 -0500 Received: from mx0a-0031df01.pphosted.com (mx0a-0031df01.pphosted.com [205.220.168.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CFEA183; Tue, 5 Dec 2023 18:25:28 -0800 (PST) Received: from pps.filterd (m0279867.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 3B60pgVZ031137; Wed, 6 Dec 2023 02:25:18 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; h=message-id : date : mime-version : subject : to : cc : references : from : in-reply-to : content-type : content-transfer-encoding; s=qcppdkim1; bh=L19f+ajkxWRfKvLtDMERO9Kn8Y9ELWUmoU2rLGScHyo=; b=G1XHVcY1aU5u93YzciAFeiioC60SiLWCvGpthsRnwJaDLevdujFWTLhNFC0+aBAaV+yM JrYNIG/+btPKM+wxrlaaWPIOoRQMxYdXk4K/NOWa/GCDlrhTcVGvmPiUJXJi3qAR04pk W0VIterumwt6TcztdsXvJpAYV0EKIwgMrp7tsafYy5dja1NNTJ84+asJ8XYLSfw1XAq8 aJ1A1Tjc8sZQ03AVJk/ft/Mb103LVuXSHPVnmi3nLJqobQtPdzVO6CqTKaPrZO52JN6t sA11Ig8GxLjfooM3FQop3f9XlA+qxHXCqJQplZfoPlBdT6bdf8ytFlq0uUkHSjSkajiZ 0Q== Received: from nasanppmta03.qualcomm.com (i-global254.qualcomm.com [199.106.103.254]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3utd0qgccx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 06 Dec 2023 02:25:17 +0000 Received: from nasanex01b.na.qualcomm.com (nasanex01b.na.qualcomm.com [10.46.141.250]) by NASANPPMTA03.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 3B62PHnd031217 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 6 Dec 2023 02:25:17 GMT Received: from [10.253.14.249] (10.80.80.8) by nasanex01b.na.qualcomm.com (10.46.141.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Tue, 5 Dec 2023 18:25:15 -0800 Message-ID: <9873ee7b-7ef1-4327-8e22-49e1cd3872f1@quicinc.com> Date: Wed, 6 Dec 2023 10:25:12 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/4] bus: mhi: host: Drop chan lock before queuing buffers Content-Language: en-US To: Manivannan Sadhasivam CC: , , , , , References: <1699939661-7385-1-git-send-email-quic_qianyu@quicinc.com> <1699939661-7385-3-git-send-email-quic_qianyu@quicinc.com> <20231124100403.GA4536@thinkpad> <639d6008-bdfa-4b6e-b622-e916003ec908@quicinc.com> <20231128133252.GX3088@thinkpad> <5eb0a521-0b72-4d15-9a65-429c4c123833@quicinc.com> <20231130053157.GB3043@thinkpad> From: Qiang Yu In-Reply-To: <20231130053157.GB3043@thinkpad> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01b.na.qualcomm.com (10.46.141.250) To nasanex01b.na.qualcomm.com (10.46.141.250) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: Ai0hCukKgEy8vzX3NDT88uu5EAFybPoP X-Proofpoint-ORIG-GUID: Ai0hCukKgEy8vzX3NDT88uu5EAFybPoP X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.997,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-12-06_01,2023-12-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 impostorscore=0 bulkscore=0 mlxlogscore=750 lowpriorityscore=0 spamscore=0 adultscore=0 priorityscore=1501 suspectscore=0 malwarescore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2312060018 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/30/2023 1:31 PM, Manivannan Sadhasivam wrote: > On Wed, Nov 29, 2023 at 11:29:07AM +0800, Qiang Yu wrote: >> On 11/28/2023 9:32 PM, Manivannan Sadhasivam wrote: >>> On Mon, Nov 27, 2023 at 03:13:55PM +0800, Qiang Yu wrote: >>>> On 11/24/2023 6:04 PM, Manivannan Sadhasivam wrote: >>>>> On Tue, Nov 14, 2023 at 01:27:39PM +0800, Qiang Yu wrote: >>>>>> Ensure read and write locks for the channel are not taken in succession by >>>>>> dropping the read lock from parse_xfer_event() such that a callback given >>>>>> to client can potentially queue buffers and acquire the write lock in that >>>>>> process. Any queueing of buffers should be done without channel read lock >>>>>> acquired as it can result in multiple locks and a soft lockup. >>>>>> >>>>> Is this patch trying to fix an existing issue in client drivers or a potential >>>>> issue in the future drivers? >>>>> >>>>> Even if you take care of disabled channels, "mhi_event->lock" acquired during >>>>> mhi_mark_stale_events() can cause deadlock, since event lock is already held by >>>>> mhi_ev_task(). >>>>> >>>>> I'd prefer not to open the window unless this patch is fixing a real issue. >>>>> >>>>> - Mani >>>> In [PATCH v4 1/4] bus: mhi: host: Add spinlock to protect WP access when >>>> queueing >>>> TREs,  we add >>>> write_lock_bh(&mhi_chan->lock)/write_unlock_bh(&mhi_chan->lock) >>>> in mhi_gen_tre, which may be invoked as part of mhi_queue in client xfer >>>> callback, >>>> so we have to use read_unlock_bh(&mhi_chan->lock) here to avoid acquiring >>>> mhi_chan->lock >>>> twice. >>>> >>>> Sorry for confusing you. Do you think we need to sqush this two patch into >>>> one? >>> Well, if patch 1 is introducing a potential deadlock, then we should fix patch >>> 1 itself and not introduce a follow up patch. >>> >>> But there is one more issue that I pointed out in my previous reply. >> Sorry, I can not understand why "mhi_event->lock" acquired during >> mhi_mark_stale_events() can cause deadlock. In mhi_ev_task(), we will >> not invoke mhi_mark_stale_events(). Can you provide some interpretation? > Going by your theory that if a channel gets disabled while processing the event, > the process trying to disable the channel will try to acquire "mhi_event->lock" > which is already held by the process processing the event. > > - Mani OK, I get you. Thank you for kind explanation. Hopefully I didn't intrude too much. > >>> Also, I'm planning to cleanup the locking mess within MHI in the coming days. >>> Perhaps we can revisit this series at that point of time. Will that be OK for >>> you? >> Sure, that will be great. >>> - Mani >>> >>>>>> Signed-off-by: Qiang Yu >>>>>> --- >>>>>> drivers/bus/mhi/host/main.c | 4 ++++ >>>>>> 1 file changed, 4 insertions(+) >>>>>> >>>>>> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c >>>>>> index 6c6d253..c4215b0 100644 >>>>>> --- a/drivers/bus/mhi/host/main.c >>>>>> +++ b/drivers/bus/mhi/host/main.c >>>>>> @@ -642,6 +642,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl, >>>>>> mhi_del_ring_element(mhi_cntrl, tre_ring); >>>>>> local_rp = tre_ring->rp; >>>>>> + read_unlock_bh(&mhi_chan->lock); >>>>>> + >>>>>> /* notify client */ >>>>>> mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result); >>>>>> @@ -667,6 +669,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl, >>>>>> kfree(buf_info->cb_buf); >>>>>> } >>>>>> } >>>>>> + >>>>>> + read_lock_bh(&mhi_chan->lock); >>>>>> } >>>>>> break; >>>>>> } /* CC_EOT */ >>>>>> -- >>>>>> 2.7.4 >>>>>> >>>>>>