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=-14.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 5CB30C4338F for ; Tue, 27 Jul 2021 23:10:01 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 287C260EB2 for ; Tue, 27 Jul 2021 23:10:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 287C260EB2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=8+HJAwSWk2qvBHukeslOYECCEtNeIuHbMdB2iSgRISA=; b=TOSXbK1dzwDgyo 28Tlzf/6wGU18rFsXe2txIT9XSZWdewM1s6lFKKbPmAtA0NMXGDOco8S+DDyUMxFHpPzm3Sl2W0Sm doB/RyuoJGACDtfinHYOrHaFntNd9t+BJRjPkSkEUl0ikT3PgGlw+GOA1CSS56WiewKOMFfgxTN0A 4m8N62tkEw2dl+k/+R3xXTLNITB9Z2aUElrRahODc1mz44Lhn9irGDyvkkGYisSjkeJ2FIVROmSUf 6+QIJsYE1Toju35i9OKEKzbV9GfLEolkVeGnnZVR4X9JjE7jNTEtEEmH66PWKF3vRmWKilRqZUJGO h4Dnrzsnng2F60qFvmGg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1m8WBR-00Gchl-CL; Tue, 27 Jul 2021 23:08:21 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1m8WBO-00Gcgg-2r for linux-arm-kernel@lists.infradead.org; Tue, 27 Jul 2021 23:08:19 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id AF79F60EB2; Tue, 27 Jul 2021 23:08:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1627427297; bh=fGzQ1yxz3VodJVrSOBzAcSVWcjc+avK52D1CDLlbVEA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XGjLo5NK3LAP03NixFWTa/BVZ0L+YJ8vcQXLdfXsz/VIGe2B0qk684NU5Q0AQJmSW JBUY/FQtGmx/2CsyIf21zVm0fhs8xBAw18Duo0myWqc+xGnINpjwsOLuhkVH6XdpsC k8lz89BOs5lR+0fmScyn4rAWRcTwQFWHgqknjVwfOOyjwVCZYcxUPuSjuBNDvADPbs uC5fh5f2eSmLo+VYMMn6Z6/N/CMgPIZxO27xBNBkIxUECfDdLV3Jj+K/zf+Vdt8B9m 8r7LA5Ek1jascxDILuJhUFvxttj2E+fdT+0NZbcX4cN7J84d/IGnGR9/qLZsDeVTbj 0a0HV9Vzw/dAA== Date: Wed, 28 Jul 2021 01:08:14 +0200 From: Frederic Weisbecker To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rt-users@vger.kernel.org, Catalin Marinas , Will Deacon , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Steven Rostedt , Daniel Bristot de Oliveira , "Paul E. McKenney" , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , Anshuman Khandual , Vincenzo Frascino , Steven Price , Ard Biesheuvel Subject: Re: [PATCH 2/3] rcu/nocb: Check for migratability rather than pure preemptability Message-ID: <20210727230814.GC283787@lothringen> References: <20210721115118.729943-1-valentin.schneider@arm.com> <20210721115118.729943-3-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210721115118.729943-3-valentin.schneider@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210727_160818_209132_9D2F8B5A X-CRM114-Status: GOOD ( 15.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 21, 2021 at 12:51:17PM +0100, Valentin Schneider wrote: > Signed-off-by: Valentin Schneider > --- > kernel/rcu/tree_plugin.h | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index ad0156b86937..6c3c4100da83 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -70,8 +70,7 @@ static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) > !(lockdep_is_held(&rcu_state.barrier_mutex) || > (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) || > rcu_lockdep_is_held_nocb(rdp) || > - (rdp == this_cpu_ptr(&rcu_data) && > - !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) || > + (rdp == this_cpu_ptr(&rcu_data) && is_pcpu_safe()) || I fear that won't work. We really need any caller of rcu_rdp_is_offloaded() on the local rdp to have preemption disabled and not just migration disabled, because we must protect against concurrent offloaded state changes. The offloaded state is changed by a workqueue that executes on the target rdp. Here is a practical example where it matters: CPU 0 ----- // =======> task rcuc running rcu_core { rcu_nocb_lock_irqsave(rdp, flags) { if (!rcu_segcblist_is_offloaded(rdp->cblist)) { // is not offloaded right now, so it's going // to just disable IRQs. Oh no wait: // preemption // ========> workqueue running rcu_nocb_rdp_offload(); // ========> task rcuc resume local_irq_disable(); } } .... rcu_nocb_unlock_irqrestore(rdp, flags) { if (rcu_segcblist_is_offloaded(rdp->cblist)) { // is offloaded right now so: raw_spin_unlock_irqrestore(rdp, flags); And that will explode because that's an impaired unlock on nocb_lock. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel