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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 66E19C433DB for ; Thu, 18 Feb 2021 05:41:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 27C2C64DF0 for ; Thu, 18 Feb 2021 05:41:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230495AbhBRFkJ (ORCPT ); Thu, 18 Feb 2021 00:40:09 -0500 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:58856 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230481AbhBRFbY (ORCPT ); Thu, 18 Feb 2021 00:31:24 -0500 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id 07AD82ACC2; Thu, 18 Feb 2021 00:30:33 -0500 (EST) Date: Thu, 18 Feb 2021 16:30:20 +1100 (AEDT) From: Finn Thain To: "Song Bao Hua (Barry Song)" cc: Arnd Bergmann , "tglx@linutronix.de" , "gregkh@linuxfoundation.org" , "arnd@arndb.de" , "geert@linux-m68k.org" , "funaho@jurai.org" , "philb@gnu.org" , "corbet@lwn.net" , "mingo@redhat.com" , "linux-m68k@lists.linux-m68k.org" , "linux-kernel@vger.kernel.org" Subject: RE: [RFC] IRQ handlers run with some high-priority interrupts(not NMI) enabled on some platform In-Reply-To: <0c0ea8eca77c45ea89f2d4432580211c@hisilicon.com> Message-ID: <28d4b91d-1774-a8a-df97-7ac9b365c2@telegraphics.com.au> References: <24e0652b3afa48cdbf7c83287e43c087@hisilicon.com> <0b766dba0b004ced94131e158cd8e67d@hisilicon.com> <5148eb2aaceb42d78087bc6d8ce15183@hisilicon.com> <5fcea94e-6fc9-c340-d7d2-4ae8b69890b8@telegraphics.com.au> <0c0ea8eca77c45ea89f2d4432580211c@hisilicon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 17 Feb 2021, Song Bao Hua (Barry Song) wrote: > > On Sat, 13 Feb 2021, Song Bao Hua (Barry Song) wrote: > > > > > > > > So what is really confusing and a pain to me is that: For years > > > people like me have been writing device drivers with the idea that > > > irq handlers run with interrupts disabled after those commits in > > > genirq. So I don't need to care about if some other IRQs on the same > > > cpu will jump out to access the data the current IRQ handler is > > > accessing. > > > > > > but it turns out the assumption is not true on some platform. So > > > should I start to program devices driver with the new idea > > > interrupts can actually come while irqhandler is running? > > > > > > That's the question which really bothers me. > > > > > > > That scenario seems a little contrived to me (drivers for two or more > > devices sharing state through their interrupt handlers). Is it real? I > > suppose every platform has its quirks. The irq lock in > > sonic_interrupt() is only there because of a platform quirk (the same > > device can trigger either of two IRQs). Anyway, no-one expects all > > drivers to work on all platforms; I don't know why it bothers you so > > much when platforms differ. > > Basically, we wrote drivers with the assumption that this driver will be > cross-platform. (Of course there are some drivers which can only work on > one platform, for example, if the IP of the device is only used in one > platform as an internal component of a specific SoC.) > > So once a device has two or more interrupts, we need to consider one > interrupt might preempt another one on m68k on the same cpu if we also > want to support this driver on m68k. this usually doesn't matter on > other platforms. > When users show up who desire to run your drivers on their platform, you can expect them to bring patches and a MAINTAINERS file entry. AFAIK, Linux development has always worked that way. Besides, not all m68k platforms implement priority masking. So there's no problem with portability to m68k per se. > on the other hand, there are more than 400 irqs_disabled() in kernel, I > am really not sure if they are running with the knowledge that the true > irqs_disabled() actually means some interrupts are off and some others > are still open on m68k. Firstly, use of irqs_disabled() is considered an antipattern by some developers. Please see, https://lore.kernel.org/linux-scsi/X8pfD5XtLoOygdez@lx-t490/ and commit e6b6be53ec91 ("Merge branch 'net-in_interrupt-cleanup-and-fixes'") This means that the differences in semantics between the irqs_disabled() implementations on various architectures are moot. Secondly, the existence of irqs_disabled() call sites does not imply a flaw in your drivers nor in the m68k interrupt scheme. The actual semantic differences are immaterial at many (all?) of these call sites. > Or they are running with the assumption that the true irqs_disabled() > means IRQ is totally quiet? If the latter is true, those drivers might > fail to work on m68k as well. > Yes it's possible, and that was my fear too back in 2017 when I raised the same question with the m68k maintainer. But I never found any code making that assumption. If you know of such a bug, do tell. So far, your fears remain unfounded. > Thanks > Barry >