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=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 AD31DC433EF for ; Wed, 15 Sep 2021 23:34:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9614961244 for ; Wed, 15 Sep 2021 23:34:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233369AbhIOXfj (ORCPT ); Wed, 15 Sep 2021 19:35:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:60452 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232929AbhIOXfE (ORCPT ); Wed, 15 Sep 2021 19:35:04 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3C55661207; Wed, 15 Sep 2021 23:33:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1631748825; bh=BjlXYbFOl31ev3C3Ez5YMdXPBUC8U17GefDyk4NGw1I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TTYF/hgJKli+PvqZINZwE/KzXmO1/0rHy6Y/7oB+bhqMf9sAEUT73SbG0ealWC+YI LLlEgy1ZbXz43Fo8YskisB0o8h8erc4ljlwSPmOi8wqbIDeUh+bHZvjEdTcx+MWd2e u2kGWU0EztbODBqBsCWtzdNuct1rxTq4Yc2y2MM7eavzMgRR/vEYLZ+qBSSwFByD9e EGGCXAFI6E3VegLH6rHW9OFR2UwYiuWp91lF4NkCGMqrtsaeQ3iLjNiPSbZV5nrpvJ nbQSkZnpNhHRFRtyt3vWzLbFL4ciFnEYJysmS8t2TT1Ws78ecbRqhWy+kzfNXmLj7H lJJB0JccMRhAA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id C709A5C09F9; Wed, 15 Sep 2021 16:33:44 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.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 rcu 07/14] rcu: Comment rcu_gp_init() code waiting for CPU-hotplug operations Date: Wed, 15 Sep 2021 16:33:36 -0700 Message-Id: <20210915233343.3906738-7-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20210915233305.GA3906641@paulmck-ThinkPad-P17-Gen-1> References: <20210915233305.GA3906641@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Near the beginning of rcu_gp_init() is a per-rcu_node loop that waits for CPU-hotplug operations that might have started before the new grace period did. This commit adds a comment explaining that this wait does not exclude CPU-hotplug operations. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0bfebec94277..e6e1b9281530 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1775,6 +1775,8 @@ static noinline_for_stack bool rcu_gp_init(void) */ WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF); rcu_for_each_leaf_node(rnp) { + // Wait for CPU-hotplug operations that might have + // started before this grace period did. smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values. firstseq = READ_ONCE(rnp->ofl_seq); if (firstseq & 0x1) -- 2.31.1.189.g2e36527f23