From patchwork Thu Sep 3 13:53:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 11753927 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B43DC722 for ; Thu, 3 Sep 2020 14:59:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88D2D20716 for ; Thu, 3 Sep 2020 14:59:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="j+QW6nUz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729209AbgICO7p (ORCPT ); Thu, 3 Sep 2020 10:59:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729101AbgICOHH (ORCPT ); Thu, 3 Sep 2020 10:07:07 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E4685C0610E3; Thu, 3 Sep 2020 06:54:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=HMKdcBAh3Qfsb0YqV9KE1AdBeTa9W/Y2t3RJ7FugT60=; b=j+QW6nUzroNn72HmxKzqjWDO5S NWwyKermXl6fL1UShM1HWUPvHIV2VIC61NK+tJPlQRgbUknfX0vL45DhVcnFsWSUHk8HyK/8ECR1j 8+8hm8yUaQRdj6wv2p+8RHIZ28gNkNG1iXSl0/vv0liO/UhJx2SDdQnywRYDUxMehPBrvx+dElVDu +G3fDh/zuuQs1ELn9WRIGouAYkJXP2cZI3UadK89ovYuIhezQzpPZp5Ik3CKgqCxrX0hXW08muef1 0tTDaI96K+tEE1jjCVH5g6SluGC4xrhyijttNv08u4guRe3iaUCPcfKe47q1uJ6mgOrT/0lKotz6o 4x4yk5pg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kDpgU-0002gF-IL; Thu, 03 Sep 2020 13:53:51 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id B8EFE300F7A; Thu, 3 Sep 2020 15:53:47 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9ABEA2BB8B563; Thu, 3 Sep 2020 15:53:47 +0200 (CEST) Date: Thu, 3 Sep 2020 15:53:47 +0200 From: peterz@infradead.org To: Ulf Hansson Cc: "Paul E. McKenney" , Lina Iyer , Naresh Kamboju , "Rafael J. Wysocki" , Saravana Kannan , open list , linux-mmc , lkft-triage@lists.linaro.org, rcu@vger.kernel.org, Linux PM , Anders Roxell , Arnd Bergmann , Rajendra Nayak , John Stultz , Stephen Boyd , Lars Povlsen , madhuparnabhowmik10@gmail.com, Viresh Kumar , Vincent Guittot , Thomas Gleixner Subject: [RFC][PATCH] cpu_pm: Remove RCU abuse Message-ID: <20200903135347.GC1362448@hirez.programming.kicks-ass.net> References: <20200901104206.GU1362448@hirez.programming.kicks-ass.net> <20200901154417.GD20303@codeaurora.org> <20200901155014.GF2674@hirez.programming.kicks-ass.net> <20200901161340.GC29330@paulmck-ThinkPad-P72> <20200901174216.GJ29142@worktop.programming.kicks-ass.net> <20200902121355.GE1362448@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Sender: linux-mmc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mmc@vger.kernel.org On Wed, Sep 02, 2020 at 05:58:55PM +0200, Ulf Hansson wrote: > On Wed, 2 Sep 2020 at 14:14, wrote: > > > > On Wed, Sep 02, 2020 at 09:03:37AM +0200, Ulf Hansson wrote: > > > Lots of cpuidle drivers are using CPU_PM notifiers (grep for > > > cpu_pm_enter and you will see) from their idlestates ->enter() > > > callbacks. And for those we are already calling > > > rcu_irq_enter_irqson|off() in cpu_pm_notify() when firing them. > > > > Yeah, that particular trainwreck is on my todo list already ... then > > again, that list is forever overflowing. > > > > I'm thinking cpu_pm_unregister_notifier() is not a common thing? The few > > I looked at seem to suggest 'never' is a good approximation. > > The trend is that drivers are turning into regular modules that may > also need to manage "->remove()", which may mean unregistering the > notifier. Of course, I don't know for sure whether that becomes a > problem, but it seems quite limiting. You can pin modules, once they're loaded they can never be removed again. Anyway, the below should 'work', I think. diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c index f7e1d0eccdbc..72804e0883d5 100644 --- a/kernel/cpu_pm.c +++ b/kernel/cpu_pm.c @@ -12,21 +12,18 @@ #include #include #include +#include +#include -static ATOMIC_NOTIFIER_HEAD(cpu_pm_notifier_chain); +static RAW_NOTIFIER_HEAD(cpu_pm_notifier_chain); +static DEFINE_SPINLOCK(cpu_pm_lock); static int cpu_pm_notify(enum cpu_pm_event event) { int ret; - /* - * atomic_notifier_call_chain has a RCU read critical section, which - * could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let - * RCU know this. - */ - rcu_irq_enter_irqson(); - ret = atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL); - rcu_irq_exit_irqson(); + lockdep_assert_irqs_disabled(); + ret = raw_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL); return notifier_to_errno(ret); } @@ -35,9 +32,8 @@ static int cpu_pm_notify_robust(enum cpu_pm_event event_up, enum cpu_pm_event ev { int ret; - rcu_irq_enter_irqson(); - ret = atomic_notifier_call_chain_robust(&cpu_pm_notifier_chain, event_up, event_down, NULL); - rcu_irq_exit_irqson(); + lockdep_assert_irqs_disabled(); + ret = raw_notifier_call_chain_robust(&cpu_pm_notifier_chain, event_up, event_down, NULL); return notifier_to_errno(ret); } @@ -54,10 +50,28 @@ static int cpu_pm_notify_robust(enum cpu_pm_event event_up, enum cpu_pm_event ev */ int cpu_pm_register_notifier(struct notifier_block *nb) { - return atomic_notifier_chain_register(&cpu_pm_notifier_chain, nb); + unsigned long flags; + int ret; + + spin_lock_irqsave(&cpu_pm_lock, flags); + ret = raw_notifier_chain_register(&cpu_pm_notifier_chain, nb); + spin_unlock_irqrestore(&cpu_pm_lock, flags); + + return ret; } EXPORT_SYMBOL_GPL(cpu_pm_register_notifier); +static bool __is_idle_cpu(int cpu, void *info) +{ + /* + * Racy as heck, however if we fail to see an idle task, it must be + * after we removed our element, so all is fine. + */ + return is_idle_task(curr_task(cpu)); +} + +static void __nop_func(void *arg) { } + /** * cpu_pm_unregister_notifier - unregister a driver with cpu_pm * @nb: notifier block to be unregistered @@ -69,7 +83,30 @@ EXPORT_SYMBOL_GPL(cpu_pm_register_notifier); */ int cpu_pm_unregister_notifier(struct notifier_block *nb) { - return atomic_notifier_chain_unregister(&cpu_pm_notifier_chain, nb); + unsigned long flags; + int ret, cpu; + + spin_lock_irqsave(&cpu_pm_lock, flags); + ret = raw_notifier_chain_unregister(&cpu_pm_notifier_chain, nb); + spin_unlock_irqrestore(&cpu_pm_lock, flags); + + /* + * Orders the removal above vs the __is_idle_cpu() test below. Matches + * schedule() switching to the idle task. + * + * Ensures that if we miss an idle task, it must be after the removal. + */ + smp_mb(); + + /* + * IPI all idle CPUs, this guarantees that no CPU is currently + * iterating the notifier list. + */ + cpus_read_lock(); + on_each_cpu_cond(__is_idle_cpu, __nop_func, NULL, 1); + cpus_read_unlock(); + + return ret; } EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier);