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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 A8A55C433E2 for ; Wed, 20 May 2020 13:28:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8796220748 for ; Wed, 20 May 2020 13:28:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="RW2QbuLn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726871AbgETN2o (ORCPT ); Wed, 20 May 2020 09:28:44 -0400 Received: from merlin.infradead.org ([205.233.59.134]:42792 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726439AbgETN2o (ORCPT ); Wed, 20 May 2020 09:28:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=6NkSTATdc+EBN2bxaA8ZPvbxxQ8lXoj7UgY/0mXcj9k=; b=RW2QbuLn9NBBL5Ykp3VpYkYVK0 2QNe8a4ubFLEZvO+Xg4Zz+fE/zYWHk6ltL6wsg/Q6fSJuiylDg5wEP/mGW5UFVVwFJPXK9uGxpkOs p1KwU6uUjytXoEbpFBIEN9k8jkh3NUFBXNP9cNFlOtYjdnmJrxxlrBNfsCmR/xi2eiwqknezBEx4h 3xfZ9PUg5TWi1rF6keaONy8Bylcx/xJf/CcA1/knUU/zBe43ZTuzP1D/Gw5v80xebfPZWhoWXw2l2 /AhcxfIcq8G996Rw56IGeY3uiKUh5Sb+Sw0/meDSw4qdNJvTiq4VktmzQn7cF4u0bgswUaDh1jfkz deF2yhmA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbOlK-0001KT-Ry; Wed, 20 May 2020 13:27:59 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C0826303DA0; Wed, 20 May 2020 15:27:55 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 1FEB029DB5053; Wed, 20 May 2020 15:27:55 +0200 (CEST) Date: Wed, 20 May 2020 15:27:55 +0200 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Steven Rostedt , Will Deacon , Thomas Gleixner , "Paul E . McKenney" , Linus Torvalds , Lai Jiangshan , Josh Triplett , Mathieu Desnoyers , rcu@vger.kernel.org Subject: Re: [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu_data access Message-ID: <20200520132755.GM317569@hirez.programming.kicks-ass.net> References: <20200519201912.1564477-1-bigeasy@linutronix.de> <20200519201912.1564477-4-bigeasy@linutronix.de> <20200520102407.GF317569@hirez.programming.kicks-ass.net> <20200520120608.mwros5jurmidxxfv@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200520120608.mwros5jurmidxxfv@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 20, 2020 at 02:06:08PM +0200, Sebastian Andrzej Siewior wrote: > On 2020-05-20 12:24:07 [+0200], Peter Zijlstra wrote: > > Would it perhaps make sense to stick the local_lock in struct srcu_data ? > > In that case we would need something for pointer stability before the > lock is acquired. Maybe I need sleep; but I think this will work. &x->foo = x + foo-offset this_cpu_ptr(x) = x + cpu-offset &this_cpu_ptr(x)->foo = (x + cpu-offset) + foo-offset = (x + foo-offset) + cpu-offset = this_cpu_ptr(&x->foo) --- --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -13,6 +13,7 @@ #include #include +#include struct srcu_node; struct srcu_struct; @@ -22,6 +23,8 @@ struct srcu_struct; * to rcu_node. */ struct srcu_data { + struct local_lock llock; + /* Read-side state. */ unsigned long srcu_lock_count[2]; /* Locks per CPU. */ unsigned long srcu_unlock_count[2]; /* Unlocks per CPU. */ --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -778,13 +778,13 @@ static bool srcu_might_be_idle(struct sr unsigned long tlast; /* If the local srcu_data structure has callbacks, not idle. */ - local_irq_save(flags); + local_lock_irqsave(&ssp->sda->llock, flags); sdp = this_cpu_ptr(ssp->sda); if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) { - local_irq_restore(flags); + local_unlock_irqrestore(&ssp->sda->llock, flags); return false; /* Callbacks already present, so not idle. */ } - local_irq_restore(flags); + local_unlock_irqrestore(&ssp->sda->llock, flags); /* * No local callbacks, so probabalistically probe global state. @@ -864,7 +864,7 @@ static void __call_srcu(struct srcu_stru } rhp->func = func; idx = srcu_read_lock(ssp); - local_irq_save(flags); + local_lock_irqsave(&ssp->sda->llock, flags); sdp = this_cpu_ptr(ssp->sda); spin_lock_rcu_node(sdp); rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); @@ -880,7 +880,8 @@ static void __call_srcu(struct srcu_stru sdp->srcu_gp_seq_needed_exp = s; needexp = true; } - spin_unlock_irqrestore_rcu_node(sdp, flags); + spin_unlock_rcu_node(sdp); + local_unlock_irqrestore(&ssp->sda->llock, flags); if (needgp) srcu_funnel_gp_start(ssp, sdp, s, do_norm); else if (needexp)