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 AD38DC001E0 for ; Mon, 23 Oct 2023 08:20:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229541AbjJWIUN (ORCPT ); Mon, 23 Oct 2023 04:20:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230090AbjJWIUL (ORCPT ); Mon, 23 Oct 2023 04:20:11 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7878FEE; Mon, 23 Oct 2023 01:20:08 -0700 (PDT) Received: from pps.filterd (m0356517.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 39N8GTQP025249; Mon, 23 Oct 2023 08:19:59 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=message-id : date : mime-version : subject : to : cc : references : from : in-reply-to : content-type : content-transfer-encoding; s=pp1; bh=XCFY9Zt73C/zdSBvzDn5qUMBCE/4dyHPB6YcoeLIraw=; b=ZgddJsDzHQOYtq6A6nqgQdZhrJkOVRI7/6nS3RwcJr8RIbK0kKgpkjbuJVjPxZFyr3PY JHFeBw+TFClQmtLjoW1nt18NGF6jCssRuh/KBa8RthSqpGMWc9NmgG+KxyE4Ozjlos2i 9JgT1/7RAKGmrY4X17BlS2xBb4COzhOoufCHwaNI4S9VC8YVI8dWCdswnS480TK6/Gxm DXWGteUptCQ1sww+3BJX5eDY70/z4cCeSykOG8xYvH5jGMDZNQM+EAz4qrH4zylMFXxu gk9D0dagWEXMSxQOr5lMZwPz6cOFdbGmTwiBAJubsC43IYmd+RLJfNTRxXnJMM8KWAwl 1g== Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3twmrhgswn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 23 Oct 2023 08:19:59 +0000 Received: from m0356517.ppops.net (m0356517.ppops.net [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 39N8GvUd028304; Mon, 23 Oct 2023 08:19:58 GMT Received: from ppma21.wdc07v.mail.ibm.com (5b.69.3da9.ip4.static.sl-reverse.com [169.61.105.91]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3twmrhgsw8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 23 Oct 2023 08:19:58 +0000 Received: from pps.filterd (ppma21.wdc07v.mail.ibm.com [127.0.0.1]) by ppma21.wdc07v.mail.ibm.com (8.17.1.19/8.17.1.19) with ESMTP id 39N7AgL3026833; Mon, 23 Oct 2023 08:19:57 GMT Received: from smtprelay03.dal12v.mail.ibm.com ([172.16.1.5]) by ppma21.wdc07v.mail.ibm.com (PPS) with ESMTPS id 3tvsynfbks-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 23 Oct 2023 08:19:57 +0000 Received: from smtpav05.dal12v.mail.ibm.com (smtpav05.dal12v.mail.ibm.com [10.241.53.104]) by smtprelay03.dal12v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 39N8JulW19661452 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 23 Oct 2023 08:19:56 GMT Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 582C758056; Mon, 23 Oct 2023 08:19:56 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C9AA058052; Mon, 23 Oct 2023 08:19:54 +0000 (GMT) Received: from [9.171.5.241] (unknown [9.171.5.241]) by smtpav05.dal12v.mail.ibm.com (Postfix) with ESMTP; Mon, 23 Oct 2023 08:19:54 +0000 (GMT) Message-ID: <83476aac-a2f6-4705-8aec-762b1f165210@linux.ibm.com> Date: Mon, 23 Oct 2023 10:19:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 5/5] net/smc: put sk reference if close work was canceled Content-Language: en-GB To: "D. Wythe" , kgraul@linux.ibm.com, jaka@linux.ibm.com, wintera@linux.ibm.com Cc: kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org References: <1697009600-22367-1-git-send-email-alibuda@linux.alibaba.com> <1697009600-22367-6-git-send-email-alibuda@linux.alibaba.com> <305c7ae2-a902-3e30-5e67-b590d848d0ba@linux.alibaba.com> <990a6b09-135a-41fb-a375-c37ffec6fe99@linux.ibm.com> <94f89147-cedc-b8b2-415f-942ec14cd670@linux.alibaba.com> From: Wenjia Zhang In-Reply-To: <94f89147-cedc-b8b2-415f-942ec14cd670@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: oiew6GEP6bnlVrDSVrvVm_dRJRq3_6Ba X-Proofpoint-GUID: jzW80NNb-lmu6XtFigsua8tCnBNmers6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-10-23_06,2023-10-19_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 mlxlogscore=999 lowpriorityscore=0 suspectscore=0 adultscore=0 malwarescore=0 impostorscore=0 spamscore=0 phishscore=0 bulkscore=0 priorityscore=1501 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2310170001 definitions=main-2310230071 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 20.10.23 04:41, D. Wythe wrote: > > > On 10/20/23 1:40 AM, Wenjia Zhang wrote: >> >> >> On 19.10.23 09:33, D. Wythe wrote: >>> >>> >>> On 10/19/23 4:26 AM, Wenjia Zhang wrote: >>>> >>>> >>>> On 17.10.23 04:06, D. Wythe wrote: >>>>> >>>>> >>>>> On 10/13/23 3:04 AM, Wenjia Zhang wrote: >>>>>> >>>>>> >>>>>> On 11.10.23 09:33, D. Wythe wrote: >>>>>>> From: "D. Wythe" >>>>>>> >>>>>>> Note that we always hold a reference to sock when attempting >>>>>>> to submit close_work. >>>>>> yes >>>>>> Therefore, if we have successfully >>>>>>> canceled close_work from pending, we MUST release that reference >>>>>>> to avoid potential leaks. >>>>>>> >>>>>> Isn't the corresponding reference already released inside the >>>>>> smc_close_passive_work()? >>>>>> >>>>> >>>>> Hi Wenjia, >>>>> >>>>> If we successfully cancel the close work from the pending state, >>>>> it means that smc_close_passive_work() has never been executed. >>>>> >>>>> You can find more details here. >>>>> >>>>> /** >>>>> * cancel_work_sync - cancel a work and wait for it to finish >>>>> * @work:the work to cancel >>>>> * >>>>> * Cancel @work and wait for its execution to finish. This function >>>>> * can be used even if the work re-queues itself or migrates to >>>>> * another workqueue. On return from this function, @work is >>>>> * guaranteed to be not pending or executing on any CPU. >>>>> * >>>>> * cancel_work_sync(&delayed_work->work) must not be used for >>>>> * delayed_work's. Use cancel_delayed_work_sync() instead. >>>>> * >>>>> * The caller must ensure that the workqueue on which @work was last >>>>> * queued can't be destroyed before this function returns. >>>>> * >>>>> * Return: >>>>> * %true if @work was pending, %false otherwise. >>>>> */ >>>>> boolcancel_work_sync(structwork_struct *work) >>>>> { >>>>> return__cancel_work_timer(work, false); >>>>> } >>>>> >>>>> Best wishes, >>>>> D. Wythe >>>> As I understand, queue_work() would wake up the work if the work is >>>> not already on the queue. And the sock_hold() is just prio to the >>>> queue_work(). That means, cancel_work_sync() would cancel the work >>>> either before its execution or after. If your fix refers to the >>>> former case, at this moment, I don't think the reference can be >>>> hold, thus it is unnecessary to put it. >>>>> >>> >>> I am quite confuse about why you think when we cancel the work before >>> its execution, >>> the reference can not be hold ? >>> >>> >>> Perhaps the following diagram can describe the problem in better way : >>> >>> smc_close_cancel_work >>> smc_cdc_msg_recv_action >>> >>> >>> sock_hold >>> queue_work >>> if (cancel_work_sync())        // successfully cancel before execution >>> sock_put()                        //  need to put it since we already >>> hold a ref before   queue_work() >>> >>> >> ha, I already thought you might ask such question:P >> >> I think here two Problems need to be clarified: >> >> 1) Do you think the bh_lock_sock/bh_unlock_sock in the >> smc_cdc_msg_recv does not protect the smc_cdc_msg_recv_action() from >> cancel_work_sync()? >> Maybe that would go back to the discussion in the other patch on the >> behaviors of the locks. >> > > Yes. bh_lock_sock/bh_unlock_sock can not block code execution protected > by lock_sock/unlock(). That is to say, they are not exclusive. > No, the logic of the inference is very vague to me. My understand is completely different. That is what I read from the kernel code. They are not *completely* exclusive, because while the bottom half context holds the lock i.e. bh_lock_sock, the process context can not get the lock by lock_sock. (This is actually my main point of my argument for these fixes, and I didn't see any clarify from you). However, while the process context holds the lock by lock_sock, the bottom half context can still get it by bh_lock_sock, this is just like what you showed in the code in lock_sock. Once it gets the ownership, it release the spinlock. > We can use a very simple example to infer that since bh_lock_sock is > type of spin-lock, if bh_lock_sock/bh_unlock_sock can block > lock_sock/unlock(), > then lock_sock/unlock() can also block bh_lock_sock/bh_unlock_sock. > > If this is true, when the process context already lock_sock(), the > interrupt context must wait for the process to call > release_sock(). Obviously, this is very unreasonable. > > >> 2) If the queue_work returns true, as I said in the last main, the >> work should be (being) executed. How could the cancel_work_sync() >> cancel the work before execution successgully? > > No, that's not true. In fact, if queue_work returns true, it simply > means that we have added the task to the queue and may schedule a worker > to execute it, > but it does not guarantee that the task will be executed or is being > executed when it returns true, > the task might still in the list and waiting some worker to execute it. > > We can make a simple inference, > > 1. A known fact is that if no special flag (WORK_UNBOUND) is given, > tasks submitted will eventually be executed on the CPU where they were > submitted. > > 2. If the queue_work returns true, the work should be or is being executed > > If all of the above are true, when we invoke queue_work in an interrupt > context, does it mean that the submitted task will be executed in the > interrupt context? > > > Best wishes, > D. Wythe > If you say the thread is not gauranteed to be waken up in then queue_work to execute the work, please explain what the kick_pool function does. However, the spin_lock understanding is still the key problem in the cases. As I said, if it is not get clarify, we don't really need to go on to disucss this. >> >>>>>>> Fixes: 42bfba9eaa33 ("net/smc: immediate termination for SMCD >>>>>>> link groups") >>>>>>> Signed-off-by: D. Wythe >>>>>>> --- >>>>>>>   net/smc/smc_close.c | 3 ++- >>>>>>>   1 file changed, 2 insertions(+), 1 deletion(-) >>>>>>> >>>>>>> diff --git a/net/smc/smc_close.c b/net/smc/smc_close.c >>>>>>> index 449ef45..10219f5 100644 >>>>>>> --- a/net/smc/smc_close.c >>>>>>> +++ b/net/smc/smc_close.c >>>>>>> @@ -116,7 +116,8 @@ static void smc_close_cancel_work(struct >>>>>>> smc_sock *smc) >>>>>>>       struct sock *sk = &smc->sk; >>>>>>>         release_sock(sk); >>>>>>> -    cancel_work_sync(&smc->conn.close_work); >>>>>>> +    if (cancel_work_sync(&smc->conn.close_work)) >>>>>>> +        sock_put(sk); >>>>>>> cancel_delayed_work_sync(&smc->conn.tx_work); >>>>>>>       lock_sock(sk); >>>>>>>   } >>>>> >>> >>> >