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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 07F00C433EF for ; Mon, 13 Dec 2021 13:14:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237275AbhLMNOP (ORCPT ); Mon, 13 Dec 2021 08:14:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49930 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235545AbhLMNON (ORCPT ); Mon, 13 Dec 2021 08:14:13 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 563F3C061574; Mon, 13 Dec 2021 05:14:13 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D075FB80EC5; Mon, 13 Dec 2021 13:14:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F7A3C34601; Mon, 13 Dec 2021 13:14:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639401250; bh=OVweQvmZKFfqAuaSOIp2hmI5/sL+o0R2iimYcXG2TOk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KcdygRrC0K9Su4AuW6zbwv4KhXvBB09wTuw2FiPKaeiNSwf3s8Yfp4euDDDVbGim9 439RCSaUUCm/wWLZm9saJ1LMNSuTXzOKXJ7vUgXUkGv/C+pyBZdop4IW1SqGhOF4RG VlFXeiT90lWsHNcWIVAHzllD43apcJOTy0N/1HnvpndnhMoRUUQcXt2r9Aswd8LtdL 3xQZkZLcEKKpifZWyFou7uKcWba12h4tUC9bpWtuHOO9r/WbSSyfmL9P98zCV7jpTV Nkat7lfm9lafE9GLfOT1qcdsy7XIcV6KOm9Fp2pTuc+YJjsU66JK1VYTz+OYYedzP+ yA4sXXLNbSo4g== Date: Mon, 13 Dec 2021 14:14:07 +0100 From: Frederic Weisbecker To: David Woodhouse Cc: Neeraj Upadhyay , paulmck@kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, urezki@gmail.com, boqun.feng@gmail.com Subject: Re: [PATCH v2] rcu/nocb: Handle concurrent nocb kthreads creation Message-ID: <20211213131407.GD782195@lothringen> References: <20211211170139.27711-1-quic_neeraju@quicinc.com> <6c184b9ffc5c641736d53bb7598f814d6b4c3fe0.camel@infradead.org> <601ecb12-ae2e-9608-7127-c2cddc8038a6@quicinc.com> <20211213112246.GA782195@lothringen> <984a63d4c11d04e2ee8a83fc9c61006413bf209e.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <984a63d4c11d04e2ee8a83fc9c61006413bf209e.camel@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 13, 2021 at 11:28:45AM +0000, David Woodhouse wrote: > On Mon, 2021-12-13 at 12:22 +0100, Frederic Weisbecker wrote: > > I was about to ack the patch but, should we really add code that isn't going to > > be necessary before a long while? > > Yeah, I'm torn on that. In this case it's harmless enough and it makes > the code reentrant in its own right instead of relying on the fact that > the cpuhp code won't invoke it multiple times in parallel. So I think > that's reasonable defensive programming. > The thing is that RCU code is already quite complicated. Are we even at least sure that we'll ever make CPU hotplug allow concurrent CPU onlining/offlining? This will require much more thoughts and a new hotplug concurrency infrastructure that we'll need to base RCU on. IMHO it's a bit early to handle that on hotplug individual callbacks. But anyway, let's see what Paul thinks about it...