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=-19.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 A1E9DC43214 for ; Tue, 10 Aug 2021 08:48:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82A9360234 for ; Tue, 10 Aug 2021 08:48:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237820AbhHJItD (ORCPT ); Tue, 10 Aug 2021 04:49:03 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:59814 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236844AbhHJIsw (ORCPT ); Tue, 10 Aug 2021 04:48:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628585310; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WWWfZfczx65IParlduf54SQJn/f7jfyxJXfN8MyeRwI=; b=X+gcnDxbEtivWjzPSrBUNjHhTGuxuiUh5A8qUZfKozXJ+pRStw1EsWOQ5pgGeF9p23i7DF ru7GzqdIIR5jb77lIeOqTaguVUii/BEiy4DY1YkS8ATdfsJXMlGpgQjLxth3UKND31SK1g 5skF+KwYXzsk9kSNidQm4wgpnT8rvCE= Received: from mail-ej1-f72.google.com (mail-ej1-f72.google.com [209.85.218.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-37-a6G3ROQZM1GhlKghC2WELg-1; Tue, 10 Aug 2021 04:48:29 -0400 X-MC-Unique: a6G3ROQZM1GhlKghC2WELg-1 Received: by mail-ej1-f72.google.com with SMTP id kf21-20020a17090776d5b02905af6ad96f02so1600341ejc.12 for ; Tue, 10 Aug 2021 01:48:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=WWWfZfczx65IParlduf54SQJn/f7jfyxJXfN8MyeRwI=; b=hv7m8pTZYy+nSsiFYqTVOwUMrrySS0E3aIvwr3bg6i4eoTWiNuP87VU5GX9s4O04Za HAEY4SU7qmba6urswgmiIEH7HT533EpZ1o/1dI9TxHFqwQl3IcdQRyPr1WwGg+BzJ4YJ ARP5dx4r5Wbg07ln6AcJ7ULGiGQ0VkGnH/2/gBz2i0eA002WDDl1MFKW0LHfD+Uai3fs 23POWOzazFalS1vrCmG7uUtSg7MqwaG1KWtPh57AZcCjj5ZQfbQ7zHZ5fd0cVENL25YP 7TQ9zf1Qk3v1FgVxQ9ZQSLUBXhVCnjImLceE7llaieAOTIH9FS+oq6XIL0WCoNMQo9Zx b9EQ== X-Gm-Message-State: AOAM532M0B0UCW4QZJfvMjLpmav9PnblFQn8toq9bO1zKOtt/3yVQbfC eHGl7gf8RPQT31AnUbRUzWSSNvkBdJ0hCdXeyYFceFA8gOPTnv6ObKn8gwa0f+U5xdh9nFpL9xO vW70AnIv78ERBXDMpKl4CELaR X-Received: by 2002:a17:906:c006:: with SMTP id e6mr26785997ejz.510.1628585308627; Tue, 10 Aug 2021 01:48:28 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzn80ECnujwqU7hjqyUptCj/nIeG0tDzxXAB3iqy+3raekA06q/d65FphjKgOD6D/7OJW+HXg== X-Received: by 2002:a17:906:c006:: with SMTP id e6mr26785981ejz.510.1628585308409; Tue, 10 Aug 2021 01:48:28 -0700 (PDT) Received: from localhost.localdomain.com ([151.29.52.108]) by smtp.gmail.com with ESMTPSA id la23sm6557667ejc.63.2021.08.10.01.48.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Aug 2021 01:48:27 -0700 (PDT) From: Juri Lelli To: paulmck@kernel.org, josh@joshtriplett.org Cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, peterz@infradead.org, bigeasy@linutronix.de, tglx@linutronix.de, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, rcu@vger.kernel.org, Juri Lelli Subject: [PATCH v2 1/2] rcu: Make rcu_normal_after_boot writable again Date: Tue, 10 Aug 2021 10:48:15 +0200 Message-Id: <20210810084816.155203-2-juri.lelli@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210810084816.155203-1-juri.lelli@redhat.com> References: <20210810084816.155203-1-juri.lelli@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Certain configurations (e.g., systems that make heavy use of netns) need to use synchronize_rcu_expedited() to service RCU grace periods even after boot. Even though synchronize_rcu_expedited() has been traditionally considered harmful for RT for the heavy use of IPIs, it is perfectly usable under certain conditions (e.g. nohz_full). Make rcupdate.rcu_normal_after_boot= again writeable on RT (if NO_HZ_ FULL is defined), but keep its default value to 1 (enabled) to avoid regressions. Users who need synchronize_rcu_expedited() will boot with rcupdate.rcu_normal_after_ boot=0 in the kernel cmdline. Reflect the change in synchronize_rcu_expedited_wait() by removing the WARN related to CONFIG_PREEMPT_RT. Signed-off-by: Juri Lelli --- kernel/rcu/tree_exp.h | 1 - kernel/rcu/update.c | 2 +- 2 files changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 2796084ef85a..d9e4f8eb9ae2 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -512,7 +512,6 @@ static void synchronize_rcu_expedited_wait(void) j = READ_ONCE(jiffies_till_first_fqs); if (synchronize_rcu_expedited_wait_once(j + HZ)) return; - WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)); } for (;;) { diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index c21b38cc25e9..bd551134e2f4 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -57,7 +57,7 @@ module_param(rcu_expedited, int, 0); module_param(rcu_normal, int, 0); static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT); -#ifndef CONFIG_PREEMPT_RT +#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL) module_param(rcu_normal_after_boot, int, 0); #endif #endif /* #ifndef CONFIG_TINY_RCU */ -- 2.31.1