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=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 444C5C388F7 for ; Fri, 13 Nov 2020 12:14:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DFBB322258 for ; Fri, 13 Nov 2020 12:14:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="KQ7be3Ki" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726776AbgKMMOH (ORCPT ); Fri, 13 Nov 2020 07:14:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:47664 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726716AbgKMMOA (ORCPT ); Fri, 13 Nov 2020 07:14:00 -0500 Received: from localhost.localdomain (unknown [176.167.84.141]) (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 E2B4E22252; Fri, 13 Nov 2020 12:13:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605269639; bh=vPj/s7U3ip2MnBfWZmwUmbzq2ttTvuI4uaU/9YxYAE8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KQ7be3KiTLeBXM/BT2Qb7QZneqai+5frDOj16t6mJPBE8NcqFbBSCPTmuxt/P6J+6 B++boB/JBCfvvq448M0AXW43oSUtg55XK80/LKg46YnUqeU+qCJ1l8clXDDLfr//xk /FML/MkqtlOB/vvf0fvZFlq2juHarTzYDDdmxBgU= From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Steven Rostedt , Thomas Gleixner , Mathieu Desnoyers , Boqun Feng , Lai Jiangshan , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , rcu@vger.kernel.org Subject: [PATCH 05/19] rcu/nocb: Don't deoffload an offline CPU with pending work Date: Fri, 13 Nov 2020 13:13:20 +0100 Message-Id: <20201113121334.166723-6-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201113121334.166723-1-frederic@kernel.org> References: <20201113121334.166723-1-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 Cc: Thomas Gleixner Cc: Boqun Feng --- kernel/rcu/tree_plugin.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 08eb035da9e7..5075bf219b23 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2227,6 +2227,15 @@ 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; + } + rcu_segcblist_offload(cblist, false); if (rdp->nocb_cb_sleep) { -- 2.25.1