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,URIBL_BLOCKED,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 88094C433E1 for ; Tue, 26 May 2020 16:16:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 67FFD20776 for ; Tue, 26 May 2020 16:16:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590509771; bh=xEHmgnxkxaALvBrFKBRWfnxTgnZvNpRIyAMaxbvk9wM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=DI3thWiwQqEYF3xkTiCaM1fWG/rCSWDCiIrgQuU1OAWTPCEMw7UB9kzj2Eb4pykNi Ziedu92go+V+A75zXrv5jYPHFEb7QtyrSm78I1Wx+BruY74UrusCb/DXRapy5dofVv IPhPNK4YdtPwwtcB+AW4DFzWxmU//wyLkIknqhzQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729496AbgEZQQK (ORCPT ); Tue, 26 May 2020 12:16:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:49566 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728361AbgEZQQK (ORCPT ); Tue, 26 May 2020 12:16:10 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 BC7CD20704; Tue, 26 May 2020 16:16:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590509769; bh=xEHmgnxkxaALvBrFKBRWfnxTgnZvNpRIyAMaxbvk9wM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=VHswxgcKkxeluYKiH4v4pe1MFXGcYoAXf1GpqKQveGmKrldcxpBZjx8LewLgzbLBz RFpH03Vhx5itPPALMsnhGG85iaJaDWYj7A4UuqwpH4IYFjJE2XV2s+vhVR9dd6U1yn VhoQxzd2Q3Dogj4xxfqsqB+KQ+NBgdPHU20UgtAc= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id A4DE43522A8B; Tue, 26 May 2020 09:16:09 -0700 (PDT) Date: Tue, 26 May 2020 09:16:09 -0700 From: "Paul E. McKenney" To: Sebastian Andrzej Siewior Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Ingo Molnar , Steven Rostedt , Will Deacon , Thomas Gleixner , Linus Torvalds , Lai Jiangshan , Josh Triplett , Mathieu Desnoyers , rcu@vger.kernel.org Subject: Re: [PATCH] srcu: Avoid local_irq_save() before acquiring spinlock_t Message-ID: <20200526161609.GJ2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200519201912.1564477-4-bigeasy@linutronix.de> <20200520102407.GF317569@hirez.programming.kicks-ass.net> <20200520120608.mwros5jurmidxxfv@linutronix.de> <20200520184345.GU2869@paulmck-ThinkPad-P72> <20200522151255.rtqnuk2cl3dpruou@linutronix.de> <20200522173953.GI2869@paulmck-ThinkPad-P72> <20200523150831.wdrthklakwm6wago@linutronix.de> <20200524190356.eqohmrmbilonm4u7@linutronix.de> <20200525032717.GV2869@paulmck-ThinkPad-P72> <20200526134134.5uq62linhbog43q3@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200526134134.5uq62linhbog43q3@linutronix.de> 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 Tue, May 26, 2020 at 03:41:34PM +0200, Sebastian Andrzej Siewior wrote: > SRCU disables interrupts to get a stable per-CPU pointer and then > acquires the spinlock which is in the per-CPU data structure. The > release uses spin_unlock_irqrestore(). While this is correct on a non-RT > kernel, this conflicts with the RT semantics because the spinlock is > converted to a 'sleeping' spinlock. Sleeping locks can obviously not be > acquired with interrupts disabled. > > Acquire the per-CPU pointer `ssp->sda' without disabling preemption and > then acquire the spinlock_t of the per-CPU data structure. The lock > will ensure that the data is consistent. > The added check_init_srcu_struct() is now needed because a statically > defined srcu_struct may remain uninitialized until this point and the > newly introduced locking operation requires an initialized spinlock_t. > > This change was tested for four hours with 8*SRCU-N and 8*SRCU-P without > causing any warnings. Queued, thank you!!! Thanx, Paul > Cc: Lai Jiangshan > Cc: "Paul E. McKenney" > Cc: Josh Triplett > Cc: Steven Rostedt > Cc: Mathieu Desnoyers > Cc: rcu@vger.kernel.org > Signed-off-by: Sebastian Andrzej Siewior > --- > kernel/rcu/srcutree.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 0c71505f0e19c..9459bca58c380 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -764,14 +764,15 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp) > unsigned long t; > unsigned long tlast; > > + check_init_srcu_struct(ssp); > /* If the local srcu_data structure has callbacks, not idle. */ > - local_irq_save(flags); > - sdp = this_cpu_ptr(ssp->sda); > + sdp = raw_cpu_ptr(ssp->sda); > + spin_lock_irqsave_rcu_node(sdp, flags); > if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) { > - local_irq_restore(flags); > + spin_unlock_irqrestore_rcu_node(sdp, flags); > return false; /* Callbacks already present, so not idle. */ > } > - local_irq_restore(flags); > + spin_unlock_irqrestore_rcu_node(sdp, flags); > > /* > * No local callbacks, so probabalistically probe global state. > @@ -851,9 +852,8 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, > } > rhp->func = func; > idx = srcu_read_lock(ssp); > - local_irq_save(flags); > - sdp = this_cpu_ptr(ssp->sda); > - spin_lock_rcu_node(sdp); > + sdp = raw_cpu_ptr(ssp->sda); > + spin_lock_irqsave_rcu_node(sdp, flags); > rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); > rcu_segcblist_advance(&sdp->srcu_cblist, > rcu_seq_current(&ssp->srcu_gp_seq)); > -- > 2.27.0.rc0 >