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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 E6F29C433DF for ; Mon, 25 May 2020 15:47:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B905E2078B for ; Mon, 25 May 2020 15:47:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590421651; bh=6ZI5+EOa31FmQbdlFBmWEw79uHVTHv8ArYj5YaQUIng=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=CUheIoNShg0fYEKdfQkyGjtzle+I9tucbl4NeY0JNnV4rgDHfcUROW6D2ymI5KcUI AdMHdn0wNzTWh3rn8aooGxkqIXCrn5ha2Cv22k+TaNFfR/cQYdlwr0TKQxjrkX4TYY /i0Z40m+hZY0I/d/h08YSWbZa0MKS39efPAIi6x0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391086AbgEYPrb (ORCPT ); Mon, 25 May 2020 11:47:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:54754 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390935AbgEYPra (ORCPT ); Mon, 25 May 2020 11:47:30 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 814432053B; Mon, 25 May 2020 15:47:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590421650; bh=6ZI5+EOa31FmQbdlFBmWEw79uHVTHv8ArYj5YaQUIng=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=u0IOQQkzOfJuJEsZrO/MQh1+5wnQ1uynD2OUaCBwSJw0LYmCJciyTvRi8HiQocLFY B3VKtLa2GzLvLanIC5oGbjstKA/Sdy44JlAillm5U/jc4kzu3FhHtvbYDmszYyblN2 rRz4HB7d+TiAe6LLz47sSF/oL+oqZyCnlSaQO9kM= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 1B8E8352267E; Mon, 25 May 2020 08:47:30 -0700 (PDT) Date: Mon, 25 May 2020 08:47:30 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Andrii Nakryiko , Alan Stern , parri.andrea@gmail.com, will@kernel.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, dlustig@nvidia.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, "andrii.nakryiko@gmail.com" Subject: Re: Some -serious- BPF-related litmus tests Message-ID: <20200525154730.GW2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200522003850.GA32698@paulmck-ThinkPad-P72> <20200522094407.GK325280@hirez.programming.kicks-ass.net> <20200522143201.GB32434@rowland.harvard.edu> <20200522174352.GJ2869@paulmck-ThinkPad-P72> <006e2bc6-7516-1584-3d8c-e253211c157e@fb.com> <20200525112521.GD317569@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200525112521.GD317569@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 25, 2020 at 01:25:21PM +0200, Peter Zijlstra wrote: > On Fri, May 22, 2020 at 12:38:21PM -0700, Andrii Nakryiko wrote: > > On 5/22/20 10:43 AM, Paul E. McKenney wrote: > > > On Fri, May 22, 2020 at 10:32:01AM -0400, Alan Stern wrote: > > > > > Also, what use is a spinlock that is accessed in only one thread? > > > > > > Multiple writers synchronize via the spinlock in this case. I am > > > guessing that his larger 16-hour test contended this spinlock. > > > > Yes, spinlock is for coordinating multiple producers. 2p1c cases (bounded > > and unbounded) rely on this already. 1p1c cases are sort of subsets (but > > very fast to verify) checking only consumer/producer interaction. > > Does that spinlock imply that we can now never fix that atrocious > bpf_prog_active trainwreck ? > > How does that spinlock not trigger the USED <- IN-NMI lockdep check: > > f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions") > > ? > > That is; how can you use a spinlock on the producer side at all? So even trylock is now forbidden in NMI handlers? If so, why? Thanx, Paul