From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726988AbgLAMxh (ORCPT ); Tue, 1 Dec 2020 07:53:37 -0500 Date: Tue, 1 Dec 2020 13:52:46 +0100 From: Peter Zijlstra Subject: Re: [PATCH 1/2] sched/idle: Fix arch_cpu_idle() vs tracing Message-ID: <20201201125246.GV2414@hirez.programming.kicks-ass.net> References: <20201120114145.197714127@infradead.org> <20201120114925.594122626@infradead.org> <20201130210003.GA40619@roeck-us.net> <20201201110209.GQ3040@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: List-ID: To: Sven Schnelle Cc: Guenter Roeck , rafael@kernel.org, viresh.kumar@linaro.org, mingo@kernel.org, x86@kernel.org, mark.rutland@arm.com, will@kernel.org, linux-kernel@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Christian Borntraeger , linux-s390@vger.kernel.org, Linus Torvalds On Tue, Dec 01, 2020 at 12:56:27PM +0100, Sven Schnelle wrote: > Hi Peter, > > Peter Zijlstra writes: > > > On Mon, Nov 30, 2020 at 01:00:03PM -0800, Guenter Roeck wrote: > >> On Fri, Nov 20, 2020 at 12:41:46PM +0100, Peter Zijlstra wrote: > >> > We call arch_cpu_idle() with RCU disabled, but then use > >> > local_irq_{en,dis}able(), which invokes tracing, which relies on RCU. > >> > > >> > Switch all arch_cpu_idle() implementations to use > >> > raw_local_irq_{en,dis}able() and carefully manage the > >> > lockdep,rcu,tracing state like we do in entry. > >> > > >> > (XXX: we really should change arch_cpu_idle() to not return with > >> > interrupts enabled) > >> > > >> > >> Has this patch been tested on s390 ? Reason for asking is that it causes > >> all my s390 emulations to crash. Reverting it fixes the problem. > > > > My understanding is that it changes the error on s390. Previously it > > would complain about the local_irq_enable() in arch_cpu_idle(), now it > > complains when taking an interrupt during idle. > > I looked into adding the required functionality for s390, but the code > we would need to add to entry.S is rather large - as you noted we would > have to duplicate large portions of irqentry_enter() into our code. > Given that s390 was fine before that patch, can you revert it and submit > it again during the next merge window? I'm not sure I understand how s390 was fine without it, let me consdier. Also, what's the status of ARM64, they do need this too.