From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=quicinc.com header.i=@quicinc.com header.b="PCdcqISz" Received: from mx0b-0031df01.pphosted.com (mx0b-0031df01.pphosted.com [205.220.180.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 09BADD44; Wed, 6 Dec 2023 21:27:18 -0800 (PST) Received: from pps.filterd (m0279869.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 3B74VJdx006324; Thu, 7 Dec 2023 05:27:12 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=sJtq/mf3IaDcHrZEnV/Gxwe8zGF+t6C09xMyyojnKQs=; b=PCdcqISz+1ZdhIslnfuyA/zxzGgA3fNrYl6nnZnJ0D1+G+NOpuTa3SODZmODoLbgFqp6 ZcvhagraZqtBE9eDJU4x9LMT9miYeHGne8SlSg2vVHG7opkNjFxpIjkUy8YNqZKT/nJo G3OyTYKjWH97Os+6OjVdxG7p38bXksaAyFQbr1xxxEfXubxJaO3/iZ+HIDrenIcNuJot dWpc/As+0P4NIJIiy9dwHsLmV6T8Ani5W0v0OV7zHAPAmG9A1lywMg76g823VMDUqAEk gaYB58J+2GZDMiIsMFdSndNAF9TtfuA2IhI181lEBFfoCprO/7JJzT20iOv/hLzVcLul +g== Received: from nasanppmta05.qualcomm.com (i-global254.qualcomm.com [199.106.103.254]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3uu2p88jye-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 07 Dec 2023 05:27:11 +0000 Received: from nasanex01b.na.qualcomm.com (nasanex01b.na.qualcomm.com [10.46.141.250]) by NASANPPMTA05.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 3B75RAGK011917 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 7 Dec 2023 05:27:10 GMT Received: from [10.253.35.241] (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; Wed, 6 Dec 2023 21:25:25 -0800 Message-ID: Date: Thu, 7 Dec 2023 13:25:23 +0800 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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> <9873ee7b-7ef1-4327-8e22-49e1cd3872f1@quicinc.com> <20231206134848.GG12802@thinkpad> From: Qiang Yu In-Reply-To: <20231206134848.GG12802@thinkpad> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) 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: v4W9o8s88LPsw8WWVMjZ_K60gCrzS_9F X-Proofpoint-ORIG-GUID: v4W9o8s88LPsw8WWVMjZ_K60gCrzS_9F 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=2023-12-07_03,2023-12-06_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 suspectscore=0 mlxlogscore=733 mlxscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 priorityscore=1501 impostorscore=0 spamscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2312070039 On 12/6/2023 9:48 PM, Manivannan Sadhasivam wrote: > On Wed, Dec 06, 2023 at 10:25:12AM +0800, Qiang Yu wrote: >> 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. > Not at all. Btw, did you actually encounter any issue that this patch is trying > to fix? Or just fixing based on code inspection. > > - Mani Yes, we actually meet the race issue in downstream driver. But I can not find more details about the issue. >>>>> 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 >>>>>>>> >>>>>>>>