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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 42147C4321A for ; Sat, 29 Jun 2019 18:09:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 48435216FD for ; Sat, 29 Jun 2019 18:09:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amarulasolutions.com header.i=@amarulasolutions.com header.b="AaM7OPbH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726943AbfF2SJU (ORCPT ); Sat, 29 Jun 2019 14:09:20 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:39665 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726882AbfF2SJT (ORCPT ); Sat, 29 Jun 2019 14:09:19 -0400 Received: by mail-wr1-f65.google.com with SMTP id x4so9485779wrt.6 for ; Sat, 29 Jun 2019 11:09:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=dGCfSveaXSMPHPyr6HiFB8gP3B6VLV12a1GRwVtVOXo=; b=AaM7OPbHyse5dmbOzzv/Mp3l+I/lWFNogFGJwZ+7B4x2hc8yUlXwQnV3MMevW6AUhj Q/IEj2ChQqFyrltZPhfXpEWJe+ws9kEYakg1wwz71l2vNPSbZ5cLfNJJXmOQn/hhQfze GuebjNALbpBZIvAHS5SA5TAkGwG9ZvFFJE6HU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=dGCfSveaXSMPHPyr6HiFB8gP3B6VLV12a1GRwVtVOXo=; b=HV+DzrGs81RW5gF2RE/JTUJERaLs3z2FEm5dHX7FYDJrJa8HV8zo0aXj7Mjs60kXc6 m9g0KF2LfW4OW4oZUEFR4xvZu5HzeNWUEz9Z8vrf1Z9dLSUAlGrUEiLmbzTLD6r5J87i a4/m6ZNig6D+5EKJEHR6S/OiDfXAznAoXr2Y0wk6XxOJdsepNL26PXO00kG+nA96VxZp 71td19o3QL9QvDco+g01ZMLz1WGsjrptSqP9dE3GW3ej1xYQedEZBuNSeKPIH9/iCgeT YYNSL/XeUSm86aRqO/uFDmm5VpjxlNYIWol6ApX56SQwn2i7rBuOZKJqGSlVSegOc2Fu 0y+A== X-Gm-Message-State: APjAAAVXqxFc3WwxDKeKTLOSP2ojm5K5BjrAb9Nl90Bsh9pHGHZjqhkz PPWncLur/Lv0BeX6ImS3d7TB2Q== X-Google-Smtp-Source: APXvYqxZXLH8eadFkupwd+aF37vCC2y3zYotJYmG2s02U8TEKeCcPfR6snKx9B+dO3t6ybneEZv7nA== X-Received: by 2002:adf:dcc2:: with SMTP id x2mr12350005wrm.55.1561831757558; Sat, 29 Jun 2019 11:09:17 -0700 (PDT) Received: from andrea ([93.90.167.233]) by smtp.gmail.com with ESMTPSA id o6sm13163379wra.27.2019.06.29.11.09.16 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 29 Jun 2019 11:09:16 -0700 (PDT) Date: Sat, 29 Jun 2019 20:09:10 +0200 From: Andrea Parri To: "Paul E. McKenney" Cc: Steven Rostedt , Byungchul Park , Scott Wood , Joel Fernandes , Sebastian Andrzej Siewior , rcu , LKML , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs Message-ID: <20190629180910.GA3399@andrea> References: <20190627173831.GW26519@linux.ibm.com> <20190627181638.GA209455@google.com> <20190627184107.GA26519@linux.ibm.com> <13761fee4b71cc004ad0d6709875ce917ff28fce.camel@redhat.com> <20190627203612.GD26519@linux.ibm.com> <20190628073138.GB13650@X58A-UD3R> <20190628104045.GA8394@X58A-UD3R> <20190628114411.5d9ab351@gandalf.local.home> <20190629151236.GA7862@andrea> <20190629165533.GA3112@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190629165533.GA3112@linux.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 29, 2019 at 09:55:33AM -0700, Paul E. McKenney wrote: > On Sat, Jun 29, 2019 at 05:12:36PM +0200, Andrea Parri wrote: > > Hi Steve, > > > > > As Paul stated, interrupts are synchronization points. Archs can only > > > play games with ordering when dealing with entities outside the CPU > > > (devices and other CPUs). But if you have assembly that has two stores, > > > and an interrupt comes in, the arch must guarantee that the stores are > > > done in that order as the interrupt sees it. > > > > Hopefully I'm not derailing the conversation too much with my questions > > ... but I was wondering if we had any documentation (or inline comments) > > elaborating on this "interrupts are synchronization points"? > > I don't know of any, but I would suggest instead looking at something > like the Hennessey and Patterson computer-architecture textbook. > > Please keep in mind that the rather detailed documentation on RCU is a > bit of an outlier due to the fact that there are not so many textbooks > that cover RCU. If we tried to replicate all of the relevant textbooks > in the Documentation directory, it would be quite a large mess. ;-) You know some developers considered it worth to develop formal specs in order to better understand concepts such as "synchronization" and "IRQs (processing)"! ... ;-) I still think that adding a few paragraphs (if only in informal prose) to explain that "interrupts are synchronization points" wouln't hurt. And you're right, I guess we may well start from a reference to H&P... Remark: we do have code which (while acknowledging that "interrupts are synchronization points") doesn't quite seem to "believe it", c.f., e.g., kernel/sched/membarrier.c:ipi_mb(). So, I guess the follow-up question would be "Would we better be (more) paranoid? ..." Thanks, Andrea