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=-8.6 required=3.0 tests=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_SANE_1 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 3BCBEC43141 for ; Fri, 15 Nov 2019 16:55:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 15D4520740 for ; Fri, 15 Nov 2019 16:55:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573836935; bh=JwmTtgTdpzqkRqSYYY977gdsPXkgEyQ8SYEGJsHifzE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=fXH+dqDuUnprJeDoHFI+QpJo2IHHYOKw1ZYS4euy4nToJ+2VBfdaz1fXV2Tjv0GzM rgjEM54flccim0rcj3nMuvsm4uDcE4G4/YxXEHqHu++Lz8vMfbBUqD6G9hQ3QXxjuH FOmQlFOggurrKmJNOqQAjfGfwi6PdoUz6fr3FQPk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727754AbfKOQzd (ORCPT ); Fri, 15 Nov 2019 11:55:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:59550 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727548AbfKOQzd (ORCPT ); Fri, 15 Nov 2019 11:55:33 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [199.201.64.141]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C8CDF20730; Fri, 15 Nov 2019 16:55:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573836932; bh=JwmTtgTdpzqkRqSYYY977gdsPXkgEyQ8SYEGJsHifzE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=zYR8sZLbjZRYzSHuTsPRIvU9WS3cB/r97043HkewttwdIUSC0b4Aedur/qexHj9QB sSmVA1YBj1k2w4mX1PyjgY+INtUOjFUNMRlGdi7hMlXdYVkzlNGA/ZWJ8FxGoKkKnf Jn8Z/UPQq2xZ0ZbpQNxcVAEFiFNWyebQKqGtMU0o= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 72A4235207BD; Fri, 15 Nov 2019 08:55:32 -0800 (PST) Date: Fri, 15 Nov 2019 08:55:32 -0800 From: "Paul E. McKenney" To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org Subject: Re: [PATCH V2 2/7] rcu: cleanup rcu_preempt_deferred_qs() Message-ID: <20191115165532.GW2865@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191102124559.1135-1-laijs@linux.alibaba.com> <20191102124559.1135-3-laijs@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191102124559.1135-3-laijs@linux.alibaba.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Nov 02, 2019 at 12:45:54PM +0000, Lai Jiangshan wrote: > Don't need to set ->rcu_read_lock_nesting negative, irq-protected > rcu_preempt_deferred_qs_irqrestore() doesn't expect > ->rcu_read_lock_nesting to be negative to work, it even > doesn't access to ->rcu_read_lock_nesting any more. > > It is true that NMI over rcu_preempt_deferred_qs_irqrestore() > may access to ->rcu_read_lock_nesting, but it is still safe > since rcu_read_unlock_special() can protect itself from NMI. > > Signed-off-by: Lai Jiangshan And given some form of patch #1, this one should be fine. But some long-term maintainable form of patch #1 clearly must come first. Thanx, Paul > --- > kernel/rcu/tree_plugin.h | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index aba5896d67e3..2fab8be2061f 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -552,16 +552,11 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) > static void rcu_preempt_deferred_qs(struct task_struct *t) > { > unsigned long flags; > - bool couldrecurse = t->rcu_read_lock_nesting >= 0; > > if (!rcu_preempt_need_deferred_qs(t)) > return; > - if (couldrecurse) > - t->rcu_read_lock_nesting -= RCU_NEST_BIAS; > local_irq_save(flags); > rcu_preempt_deferred_qs_irqrestore(t, flags); > - if (couldrecurse) > - t->rcu_read_lock_nesting += RCU_NEST_BIAS; > } > > /* > -- > 2.20.1 >