From patchwork Mon Mar 20 17:37:51 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 13181647 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 76369C7618A for ; Mon, 20 Mar 2023 17:43:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229754AbjCTRnB (ORCPT ); Mon, 20 Mar 2023 13:43:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229548AbjCTRmU (ORCPT ); Mon, 20 Mar 2023 13:42:20 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ECEE62FCF4; Mon, 20 Mar 2023 10:38:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=xIGBDX2EZEpc0ssKQVBXvgtW7cG0vVRXRGdmOwZy7tY=; b=tXbPP4VleH5r7CSdvSeL8/zd0i rT5Nl2nGvLYuZa12d2BS9tD6u4ajBZY8+4tU6DblhI+TEwj0ahJt6TmAtZq86fbJq5YajWtBSMPIC 2mbSafqDkRx9PsZYgv8KbIL2thuVNmgC2nEEP/lu6HjjaKYJbRr4j9uVN0NPD+Sj9bcFeQ+MpK49k DdSmFt/klha96UIcqVPyJqFrDIKyAeaziiy/UnxjakYG1+gUFYmBGDbves3Qr3CdNY5uNiJoPYPeS nkla2pc+FLuw6nHZ/VxSXhbjqoNo/VPi1XlcE7/15UoxcXFXxpf0tYqiwNPzAXwaeIIHwCcaCrKlc hve7mxWw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1peJSD-001Fqg-Jt; Mon, 20 Mar 2023 17:37:53 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 617BB300652; Mon, 20 Mar 2023 18:37:51 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2199A240AEA49; Mon, 20 Mar 2023 18:37:51 +0100 (CET) Date: Mon, 20 Mar 2023 18:37:51 +0100 From: Peter Zijlstra To: Paul McKenney , Mark Rutland , linux-kernel@vger.kernel.org Cc: frederic@kernel.org, quic_neeraju@quicinc.com, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, rcu@vger.kernel.org Subject: [PATCH] rcu: Remove RCU_NONIDLE() Message-ID: <20230320173751.GU2194297@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Since there are now exactly _zero_ users of RCU_NONIDLE(), make it go away before someone else decides to (ab)use it. Signed-off-by: Peter Zijlstra (Intel) Acked-by: Mark Rutland --- .../RCU/Design/Requirements/Requirements.rst | 36 +--------------------- Documentation/RCU/whatisRCU.rst | 1 - include/linux/rcupdate.h | 25 --------------- 3 files changed, 1 insertion(+), 61 deletions(-) diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst index 49387d823619..77155b51d4c2 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -2071,41 +2071,7 @@ call. Because RCU avoids interrupting idle CPUs, it is illegal to execute an RCU read-side critical section on an idle CPU. (Kernels built with -``CONFIG_PROVE_RCU=y`` will splat if you try it.) The RCU_NONIDLE() -macro and ``_rcuidle`` event tracing is provided to work around this -restriction. In addition, rcu_is_watching() may be used to test -whether or not it is currently legal to run RCU read-side critical -sections on this CPU. I learned of the need for diagnostics on the one -hand and RCU_NONIDLE() on the other while inspecting idle-loop code. -Steven Rostedt supplied ``_rcuidle`` event tracing, which is used quite -heavily in the idle loop. However, there are some restrictions on the -code placed within RCU_NONIDLE(): - -#. Blocking is prohibited. In practice, this is not a serious - restriction given that idle tasks are prohibited from blocking to - begin with. -#. Although nesting RCU_NONIDLE() is permitted, they cannot nest - indefinitely deeply. However, given that they can be nested on the - order of a million deep, even on 32-bit systems, this should not be a - serious restriction. This nesting limit would probably be reached - long after the compiler OOMed or the stack overflowed. -#. Any code path that enters RCU_NONIDLE() must sequence out of that - same RCU_NONIDLE(). For example, the following is grossly - illegal: - - :: - - 1 RCU_NONIDLE({ - 2 do_something(); - 3 goto bad_idea; /* BUG!!! */ - 4 do_something_else();}); - 5 bad_idea: - - - It is just as illegal to transfer control into the middle of - RCU_NONIDLE()'s argument. Yes, in theory, you could transfer in - as long as you also transferred out, but in practice you could also - expect to get sharply worded review comments. +``CONFIG_PROVE_RCU=y`` will splat if you try it.) It is similarly socially unacceptable to interrupt an ``nohz_full`` CPU running in userspace. RCU must therefore track ``nohz_full`` userspace diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst index 2c5563a91998..c3b1cbfa1530 100644 --- a/Documentation/RCU/whatisRCU.rst +++ b/Documentation/RCU/whatisRCU.rst @@ -1117,7 +1117,6 @@ in docbook. Here is the list, by category. RCU_LOCKDEP_WARN rcu_sleep_check - RCU_NONIDLE All: Unchecked RCU-protected pointer access:: diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 094321c17e48..ddd42efc6224 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -156,31 +156,6 @@ static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } static inline void rcu_nocb_flush_deferred_wakeup(void) { } #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ -/** - * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers - * @a: Code that RCU needs to pay attention to. - * - * RCU read-side critical sections are forbidden in the inner idle loop, - * that is, between the ct_idle_enter() and the ct_idle_exit() -- RCU - * will happily ignore any such read-side critical sections. However, - * things like powertop need tracepoints in the inner idle loop. - * - * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) - * will tell RCU that it needs to pay attention, invoke its argument - * (in this example, calling the do_something_with_RCU() function), - * and then tell RCU to go back to ignoring this CPU. It is permissible - * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is - * on the order of a million or so, even on 32-bit systems). It is - * not legal to block within RCU_NONIDLE(), nor is it permissible to - * transfer control either into or out of RCU_NONIDLE()'s statement. - */ -#define RCU_NONIDLE(a) \ - do { \ - ct_irq_enter_irqson(); \ - do { a; } while (0); \ - ct_irq_exit_irqson(); \ - } while (0) - /* * Note a quasi-voluntary context switch for RCU-tasks's benefit. * This is a macro rather than an inline function to avoid #include hell.