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=-10.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 B3044C433DB for ; Wed, 10 Feb 2021 03:44:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 79E5064E3B for ; Wed, 10 Feb 2021 03:44:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230379AbhBJDoJ (ORCPT ); Tue, 9 Feb 2021 22:44:09 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:12887 "EHLO szxga07-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229854AbhBJDoF (ORCPT ); Tue, 9 Feb 2021 22:44:05 -0500 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4Db5D75nRfz7j2F; Wed, 10 Feb 2021 11:41:59 +0800 (CST) Received: from [127.0.0.1] (10.40.192.131) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.498.0; Wed, 10 Feb 2021 11:43:19 +0800 Subject: Re: [Linuxarm] [PATCH for next v1 0/2] gpio: few clean up patches to replace spin_lock_irqsave with spin_lock To: Andy Shevchenko CC: Linus Walleij , Andy Shevchenko , Grygorii Strashko , Santosh Shilimkar , "Kevin Hilman" , "open list:GPIO SUBSYSTEM" , Linux Kernel Mailing List , References: <1612774577-55943-1-git-send-email-luojiaxing@huawei.com> <2b8001bb-0bcd-3fea-e15c-2722e7243209@huawei.com> <1a5dfcf2-11a2-f549-782d-447d58e21305@huawei.com> From: luojiaxing Message-ID: Date: Wed, 10 Feb 2021 11:43:19 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.40.192.131] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/2/9 17:42, Andy Shevchenko wrote: > On Tue, Feb 9, 2021 at 11:24 AM luojiaxing wrote: >> On 2021/2/8 21:28, Andy Shevchenko wrote: >>> On Mon, Feb 8, 2021 at 11:11 AM luojiaxing wrote: >>>> Sorry, my operation error causes a patch missing from this patch set. I >>>> re-send the patch set. Please check the new one. >>> What is the new one?! You have to give proper versioning and change >>> log for your series. >> sure, I will send a new one later, but let me answer your question first. >> >>>> On 2021/2/8 16:56, Luo Jiaxing wrote: >>>>> There is no need to use API with _irqsave in hard IRQ handler, So replace >>>>> those with spin_lock. >>> How do you know that another CPU in the system can't serve the > The keyword here is: *another*. ooh, sorry, now I got your point. As to me, I don't think another CPU can serve the IRQ when one CPU runing hard IRQ handler, except it's a per CPU interrupts. The following is a simple call logic when IRQ come. elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event Assume that two CPUs receive the same IRQ and enter the preceding process. Both of them will go to desc->handle_irq(). In handle_irq(), raw_spin_lock(&desc->lock) always be called first. Therefore, even if two CPUs are running handle_irq(), only one can get the spin lock. Assume that CPU A obtains the spin lock. Then CPU A will sets the status of irq_data to IRQD_IRQ_INPROGRESS in handle_irq_event() and releases the spin lock. Even though CPU B gets the spin lock later and continue to run handle_irq(), but the check of irq_may_run(desc) causes it to exit. so, I think we don't own the situation that two CPU server the hard IRQ handler at the same time. > >>> following interrupt from the hardware at the same time? >> Yes, I have some question before. >> >> There are some similar discussion here, please take a look, Song baohua >> explained it more professionally. >> >> https://lore.kernel.org/lkml/e949a474a9284ac6951813bfc8b34945@hisilicon.com/ >> >> Here are some excerpts from the discussion: >> >> I think the code disabling irq in hardIRQ is simply wrong. > Why? I mention the following call before. elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event __handle_domain_irq() will call irq_enter(), it ensures that the IRQ processing of the current CPU can not be preempted. So I think this is the reason why Song baohua said it's not need to disable IRQ in hardIRQ handler. > >> Since this commit >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e58aa3d2d0cc >> genirq: Run irq handlers with interrupts disabled >> >> interrupt handlers are definitely running in a irq-disabled context >> unless irq handlers enable them explicitly in the handler to permit >> other interrupts. > This doesn't explain any changes in the behaviour on SMP. > IRQ line can be disabled on a few stages: > a) on the source (IP that generates an event) > b) on IRQ router / controller > c) on CPU side yes, you are right. > > The commit above is discussing (rightfully!) the problem when all > interrupts are being served by a *single* core. Nobody prevents them > from being served by *different* cores simultaneously. Also, see [1]. > > [1]: https://www.kernel.org/doc/htmldocs/kernel-locking/cheatsheet.html I check [1], quite useful description about locking, thanks. But you can see Table of locking Requirements Between IRQ handler A and IRQ handle A, it's no need for a SLIS. Thanks Jiaxing >