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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,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 E301EC433E2 for ; Mon, 31 Aug 2020 18:12:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C7ACD2068E for ; Mon, 31 Aug 2020 18:12:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598897520; bh=A7Frv41HbShMLrvra7ZQ4nWH6TtbcUXyTeRPOsb0uEs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=OwMhxCrgYUKKXPQbXRQhAytgfGSXOl2UQ4lu0EEDAt9M/ABfhjJFATkRwqDsWlPUZ I8UgLhzTZXWPzJpj71qH4TQ+FRRPlIyasRSffj33hcjinZLBGr9xHQbsEmj/E1JwOC jC84F5FcbSaF0tagtBva6lmnfx49OtrOhO25UH9c= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729434AbgHaSLq (ORCPT ); Mon, 31 Aug 2020 14:11:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:36206 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729252AbgHaSL0 (ORCPT ); Mon, 31 Aug 2020 14:11:26 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E635521534; Mon, 31 Aug 2020 18:11:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598897484; bh=A7Frv41HbShMLrvra7ZQ4nWH6TtbcUXyTeRPOsb0uEs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SLODH/yZ6DD3ej7n84BRKv+ehFz/gv4epQODy9/5hkj1Vncg31R05Zpln6e+rtkBa HdpFM4Js6AZAQGH3IJa2wOK0uWRSLQcVtGYPYllFfWkJsy3CdDRT21IS91IqSNGpwy Y+GnpCAuVFNytDgMmmcCqJeCvK2iKtx4f7q2U6X8= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 11/13] rcu: Execute RCU reader shortly after rcu_core for strict GPs Date: Mon, 31 Aug 2020 11:11:18 -0700 Message-Id: <20200831181120.1044-11-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200831181101.GA950@paulmck-ThinkPad-P72> References: <20200831181101.GA950@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Paul E. McKenney" A kernel built with CONFIG_RCU_STRICT_GRACE_PERIOD=y needs a quiescent state to appear very shortly after a CPU has noticed a new grace period. Placing an RCU reader immediately after this point is ineffective because this normally happens in softirq context, which acts as a big RCU reader. This commit therefore introduces a new per-CPU work_struct, which is used at the end of rcu_core() processing to schedule an RCU read-side critical section from within a clean environment. Reported-by Jann Horn Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 13 +++++++++++++ kernel/rcu/tree.h | 1 + 2 files changed, 14 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 4bbedfc..31995b3 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2646,6 +2646,14 @@ void rcu_force_quiescent_state(void) } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); +// Workqueue handler for an RCU reader for kernels enforcing struct RCU +// grace periods. +static void strict_work_handler(struct work_struct *work) +{ + rcu_read_lock(); + rcu_read_unlock(); +} + /* Perform RCU core processing work for the current CPU. */ static __latent_entropy void rcu_core(void) { @@ -2690,6 +2698,10 @@ static __latent_entropy void rcu_core(void) /* Do any needed deferred wakeups of rcuo kthreads. */ do_nocb_deferred_wakeup(rdp); trace_rcu_utilization(TPS("End RCU core")); + + // If strict GPs, schedule an RCU reader in a clean environment. + if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) + queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work); } static void rcu_core_si(struct softirq_action *h) @@ -3887,6 +3899,7 @@ rcu_boot_init_percpu_data(int cpu) /* Set up local state, ensuring consistent view of global state. */ rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu); + INIT_WORK(&rdp->strict_work, strict_work_handler); WARN_ON_ONCE(rdp->dynticks_nesting != 1); WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp))); rdp->rcu_ofl_gp_seq = rcu_state.gp_seq; diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index c96ae35..5831ac0 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -164,6 +164,7 @@ struct rcu_data { /* period it is aware of. */ struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */ bool defer_qs_iw_pending; /* Scheduler attention pending? */ + struct work_struct strict_work; /* Schedule readers for strict GPs. */ /* 2) batch handling */ struct rcu_segcblist cblist; /* Segmented callback list, with */ -- 2.9.5