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,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 DD5CAC4363A for ; Fri, 23 Oct 2020 14:48:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7EA102168B for ; Fri, 23 Oct 2020 14:48:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603464480; bh=jxFG6MHUZbunBKZRg4SeYrw205Zm76tdAI9U5nNICn0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=C/0nh2R3oJw1TJk0WbAJXhPlKwBTytLw1EXxGsISlxOAicMDzkBqiwbEQp3l1BZy4 s+m6iiM4HSWn8N4c1K8np1l1kMRXQ7bUsFW+EvuOlHTfYbbRtdjbaUUtPgTqxJ+8Kn YOfg0FuwOGqFStV+xZDHUVviy8FH+i83e7rjSihA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750819AbgJWOr6 (ORCPT ); Fri, 23 Oct 2020 10:47:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:33202 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750734AbgJWOrM (ORCPT ); Fri, 23 Oct 2020 10:47:12 -0400 Received: from localhost.localdomain (unknown [176.167.163.208]) (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 5318A22460; Fri, 23 Oct 2020 14:47:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603464431; bh=jxFG6MHUZbunBKZRg4SeYrw205Zm76tdAI9U5nNICn0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=roslJr4WpN+Gsx6GiZNdbj0wEyalbFKlWppUjZu6gsVbxz8vMen8LaGb6rXSCnaud GCmViopYpGXajMEI19XxNOgqbMAkHmICbNG9ChusPLRySarRzG8mUFf9U0YrOVvFkb Dm6lcm+BxTnfi15JCvMAoN1nUUITsIU+QHqUnUjc= From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Steven Rostedt , Mathieu Desnoyers , "Paul E . McKenney" , Lai Jiangshan , Neeraj Upadhyay , Joel Fernandes , Josh Triplett Subject: [PATCH 06/16] rcu/nocb: Don't deoffload an offline CPU with pending work Date: Fri, 23 Oct 2020 16:46:39 +0200 Message-Id: <20201023144649.53046-7-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201023144649.53046-1-frederic@kernel.org> References: <20201023144649.53046-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Offlining offloaded CPUs don't migrate their callbacks just like non-offloaded CPUs do. It's up to their CB/GP kthread to handle what remains. Therefore we can't afford to de-offload an offline CPU that still has pending work to do, or the callbacks would be ignored. NOTE: The long term solution will be to wait for all pending callbacks to be processed before completing a CPU down operation. Suggested-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Paul E. McKenney Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Neeraj Upadhyay --- kernel/rcu/tree_plugin.h | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 09caf319a4a9..33e9d53d2181 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2228,6 +2228,14 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp) printk("De-offloading %d\n", rdp->cpu); rcu_nocb_lock_irqsave(rdp, flags); + /* + * If there are still pending work offloaded, the offline + * CPU won't help much handling them. + */ + if (cpu_is_offline(rdp->cpu) && !rcu_segcblist_empty(&rdp->cblist)) { + rcu_nocb_unlock_irqrestore(rdp, flags); + return -EBUSY; + } raw_spin_lock_rcu_node(rnp); rcu_segcblist_offload(cblist, false); raw_spin_unlock_rcu_node(rnp); -- 2.25.1