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 34956C004C0 for ; Mon, 23 Oct 2023 10:28:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230404AbjJWK2a (ORCPT ); Mon, 23 Oct 2023 06:28:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231136AbjJWK22 (ORCPT ); Mon, 23 Oct 2023 06:28:28 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C6E6D79; Mon, 23 Oct 2023 03:28:25 -0700 (PDT) Received: from pps.filterd (m0360083.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 39NAHJJv026438; Mon, 23 Oct 2023 10:28:22 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=fpYWhfGZJIbxbu2Kjyhz4Grm6wytg0wX8wN0sqL73QY=; b=mTTUA0RpHrzv0BcXz40Aj4SGdIiefSkw1sByoNBSkhn7ZVEYRJeBWDgzPt/F5CtG3x8A 705TkKKdPrk4WHfol9zDz7OHiiyVmvzCOoB/nf06fKIu7ujPBsoPscx58lzFnNCvpUBb 1HCX+j86K3nSg0XTiC09lcfyWK/hOuq8reTOKaYqJAdcNMPaaaIY08QzFdrJenSsXwDG lIzsezP6EcjcH7MnCMEB+E69MmYO+XIGBjQMKUw7GIArWxVg5fgdzq1gdOkuKl+smzxd jiGFpBabak13w9djR0ZBprlg7u8c/py8mFH9oEkMEdT6WiCnNhpPF5KsWSo+RurBlsiG eg== Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3twpxpgavy-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 23 Oct 2023 10:28:22 +0000 Received: from m0360083.ppops.net (m0360083.ppops.net [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 39NAI2GB029798; Mon, 23 Oct 2023 10:28:21 GMT Received: from ppma12.dal12v.mail.ibm.com (dc.9e.1632.ip4.static.sl-reverse.com [50.22.158.220]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3twpxpgavf-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 23 Oct 2023 10:28:21 +0000 Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.17.1.19/8.17.1.19) with ESMTP id 39N94VaA023834; Mon, 23 Oct 2023 10:28:20 GMT Received: from smtprelay05.wdc07v.mail.ibm.com ([172.16.1.72]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 3tvrysr97a-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 23 Oct 2023 10:28:20 +0000 Received: from smtpav02.dal12v.mail.ibm.com (smtpav02.dal12v.mail.ibm.com [10.241.53.101]) by smtprelay05.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 39NASJl420775632 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 23 Oct 2023 10:28:19 GMT Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3376F58051; Mon, 23 Oct 2023 10:28:19 +0000 (GMT) Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A6BD458065; Mon, 23 Oct 2023 10:28:17 +0000 (GMT) Received: from [9.171.5.241] (unknown [9.171.5.241]) by smtpav02.dal12v.mail.ibm.com (Postfix) with ESMTP; Mon, 23 Oct 2023 10:28:17 +0000 (GMT) Message-ID: Date: Mon, 23 Oct 2023 12:28:16 +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> <83476aac-a2f6-4705-8aec-762b1f165210@linux.ibm.com> <567c792e-33e0-9ff6-f5c2-0eae356c7eb1@linux.alibaba.com> From: Wenjia Zhang In-Reply-To: <567c792e-33e0-9ff6-f5c2-0eae356c7eb1@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: -uvqdCW3UUCvUE7dzYuhwZhSmIGZhtob X-Proofpoint-ORIG-GUID: TooYV33VuxTfBE8kYI2MVLcst3Esjq1A 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_09,2023-10-19_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 malwarescore=0 clxscore=1015 impostorscore=0 mlxlogscore=999 lowpriorityscore=0 phishscore=0 spamscore=0 bulkscore=0 priorityscore=1501 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2310170001 definitions=main-2310230090 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 23.10.23 10:52, D. Wythe wrote: > > > On 10/23/23 4:19 PM, Wenjia Zhang wrote: >> >> >> 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. >> > > “ while the process context holds the lock by lock_sock, the bottom half > context can still get it by bh_lock_sock,  ” > > You already got that, so why that sock_set_flag(DONE) and > sock_set_flag(DEAD) can not happen concurrently ? > Then I'd ask how do you understand this sentence I wrote? "while the bottom half context holds the lock i.e. bh_lock_sock, the process context can not get the lock by lock_sock." > >>> 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. > > I never said that. > What do you understand on the kick_pool there? >> >> 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); >>>>>>>>>   } >>>>>>> >>>>> >>>>> >>> >