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=-19.3 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,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 7BF60C433DB for ; Thu, 28 Jan 2021 17:16:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 38DDD64E1A for ; Thu, 28 Jan 2021 17:16:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232493AbhA1RQd (ORCPT ); Thu, 28 Jan 2021 12:16:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:50736 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232769AbhA1RNO (ORCPT ); Thu, 28 Jan 2021 12:13:14 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5ED1F64E18; Thu, 28 Jan 2021 17:12:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611853953; bh=c1G2wkbaXSdaflMGPDD24BHmwffEef+9SnNDPAANxEQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bCxtPw4lngaB7EITdNNQRP0tXHajdxcbSVUIIh4SKcakMnLvJf9KMtV5EqX6IsxrZ Pn/x4rCoCJF7Fvj/qfqpgsStyBx6WBkqsgNhkzzSy1KPP/RVZUNcTPI57zYP2NMstC wsChBOH3IjwqGNI6ly2X0ti/A86StcyTjNp+TWtPOnhN2K3CEPH7ecYC/KWznQwb8m bqbc8fK+FeJz7xS2iFzGibEElSK/p+6nyztzptGBhiAXPSrANQh5+Kv5f5kfm2Ntpy CgDLE1JuoMTcMEs/lmuQyskUOo9JUyQ6l5Q5LpmLrjNJLbkBmJ+934BVymlYjyhpqP hD/ptYn6cU5fg== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Boqun Feng , Lai Jiangshan , Neeraj Upadhyay , Josh Triplett , Stable , Joel Fernandes Subject: [PATCH 02/16] rcu/nocb: Comment the reason behind BH disablement on batch processing Date: Thu, 28 Jan 2021 18:12:08 +0100 Message-Id: <20210128171222.131380-3-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210128171222.131380-1-frederic@kernel.org> References: <20210128171222.131380-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Explain why we need to disable softirqs while processing callbacks in an offline fashion. The subtle reason doesn't want to be forgotten. Reported-by: Boqun Feng Reported-by: Paul E. McKenney Cc: Josh Triplett Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Neeraj Upadhyay Cc: Boqun Feng Signed-off-by: Frederic Weisbecker --- kernel/rcu/tree_plugin.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index a44f80d7661b..dcfae03eb9e9 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2235,6 +2235,12 @@ static void nocb_cb_wait(struct rcu_data *rdp) local_irq_save(flags); rcu_momentary_dyntick_idle(); local_irq_restore(flags); + /* + * While transitioning to/from NOCB mode, a CPU might execute the same + * callback concurrently if it requeues itself and the softirq interrupts + * the offloaded callback processing. Make sure we disable BH to prevent + * from that. + */ local_bh_disable(); rcu_do_batch(rdp); local_bh_enable(); -- 2.25.1