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 F3BDBC433FE for ; Mon, 3 Oct 2022 14:11:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229702AbiJCOLs (ORCPT ); Mon, 3 Oct 2022 10:11:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53386 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229646AbiJCOLq (ORCPT ); Mon, 3 Oct 2022 10:11:46 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A60F1474C4; Mon, 3 Oct 2022 07:11:45 -0700 (PDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 26036610A5; Mon, 3 Oct 2022 14:11:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28FA7C433D6; Mon, 3 Oct 2022 14:11:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664806304; bh=J9ox8N8wYu3SZufmb98XL1XtAY0TbDFRCg8d91zEJBk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=FiH84pjXaOWKhC/txvH6CAY1oJA/qMYXMApe8CN1JpUPryvqZb7Qba2L3aVn77LpD F8KFgAUhvJh1BxteHc7voXwKAPxaiIrmdsdSDMpAw53ss5TyiPKz/cJZOX+/HyQHa+ pIqVDQc/WiWqnW6vK3VxoAuhBngQJwKJKD4AE6RfVFDvc6sCQuwr1THffzdUKF74nD u8f15ju3PvJsBi/jhjWCxbzXhOSqBA29Tk6JDHZxzqpc/c9/RVRhWZsAPFzDXNvFj9 A0z4QZYE/3jHqT3rpn9QWEss4txuCiJwRaZ8DPCt2CFBTsl0R9jCfwJh6KINN/gcz+ jal5kUDLlQQJg== Date: Mon, 3 Oct 2022 16:11:41 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, tglx@linutronix.de, john.ogness@linutronix.de, pmladek@suse.com Subject: Re: [PATCH v2 rcu 0/8] NMI-safe SRCU reader API Message-ID: <20221003141141.GB306466@lothringen> References: <20220921144620.GA1200846@paulmck-ThinkPad-P17-Gen-1> <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, Sep 29, 2022 at 11:07:14AM -0700, Paul E. McKenney wrote: > Hello! > > This RFC series provides the second version of an NMI-safe SRCU reader API > in the guise of srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe(). > A given srcu_struct structure must use either the traditional > srcu_read_lock() and srcu_read_unlock() API or the new _nmisafe() API: > Mixing and matching is not permitted. So much so that kernels built > with CONFIG_PROVE_RCU=y will complain if you try it. > > The reason for this restriction is that I have yet to find a use case > that is not a accident waiting to happen. And if free intermixing > were permitted, it is pretty much a given that someone somewhere will > get confused and use srcu_read_lock_nmisafe() within NMI handlers and > srcu_read_lock() elsewhere, which will not (repeat, NOT) provide NMI > safety. > > I do not expect to push this into the v6.1 merge window. However, if > the printk() series that needs it goes in, then I will push it as a fix > for the resulting regression. > > The series is as follows: > > 1. Convert ->srcu_lock_count and ->srcu_unlock_count to atomic. > > 2. Create an srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe(). > > 3. Check for consistent per-CPU per-srcu_struct NMI safety. > > 4. Check for consistent global per-srcu_struct NMI safety. > > 5. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. > > 6. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. > > 7. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. > > 8. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. > > Changes since v1 RFC: > > 1. Added enabling patches for arm64, loongarch, s390, and x86. > These have what appear to me to be NMI-safe this_cpu_inc() > implementations. > > 2. Fix a build error on !SMP kernels built without SRCU. > > 3. Fix a build error on !SMP kernels. > > Thanx, Paul > > ------------------------------------------------------------------------ > > b/arch/arm64/Kconfig | 1 > b/arch/loongarch/Kconfig | 1 > b/arch/s390/Kconfig | 1 > b/arch/x86/Kconfig | 1 > b/include/linux/srcu.h | 39 +++++++++++++++++++++ > b/include/linux/srcutiny.h | 11 ++++++ > b/include/linux/srcutree.h | 4 +- > b/kernel/rcu/Kconfig | 3 + > b/kernel/rcu/rcutorture.c | 11 ++++-- > b/kernel/rcu/srcutree.c | 24 ++++++------- > include/linux/srcu.h | 4 +- > include/linux/srcutiny.h | 4 +- > include/linux/srcutree.h | 12 +++++- > kernel/rcu/srcutree.c | 82 +++++++++++++++++++++++++++++++++++++++------ > 14 files changed, 166 insertions(+), 32 deletions(-) Except for patches 6/7/8, for which I may miss subtle things: Reviewed-by: Frederic Weisbecker