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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7C5D4C433ED for ; Mon, 26 Apr 2021 08:31:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CF88601FD for ; Mon, 26 Apr 2021 08:31:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232356AbhDZIcX (ORCPT ); Mon, 26 Apr 2021 04:32:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232271AbhDZIcX (ORCPT ); Mon, 26 Apr 2021 04:32:23 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3AA1C061574 for ; Mon, 26 Apr 2021 01:31:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=eL8XVt5BRAXJfIlJlROfambfX03idOf5Kja4deVFnSI=; b=KjSgFVgs4vdlEnsuZCVr+vw1oq FdDpL42tXKuWdu/0Zw+rSK28+u3Nw5vk2+ZnmfYZfCMJDHf/VSl6FgWkOc3Z8Vnlp8eb8MqnJEn+E 3bU277HeR5d9gmy7N3m60IUmMjkDyQw5wFOxBVIzdrc+ErWfT/sXo+58R3bjuxGFuUP/YvqIii8Q2 FPezBobBWJeRlDKxPz9ksqDbFcADEpqIvd11xqDIgZYVb01zC20D0gX6M52me5pzaOocDyna1meNG BvfLgxRTeTqgnK4Ga0mEr0uJvw5V0SiIBtVX3F53rDGDzb2HGUjR6ZzVD0PfUIdgsneHymPKgjQ3X W9y5fIeg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1laweW-007DVe-1f; Mon, 26 Apr 2021 08:31:36 +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 (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 23D21300212; Mon, 26 Apr 2021 10:31:34 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D3DB3234E7138; Mon, 26 Apr 2021 10:31:34 +0200 (CEST) Date: Mon, 26 Apr 2021 10:31:34 +0200 From: Peter Zijlstra To: Josh Don Cc: Joel Fernandes , "Hyser,Chris" , Ingo Molnar , Vincent Guittot , Valentin Schneider , Mel Gorman , linux-kernel , Thomas Gleixner Subject: Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock Message-ID: References: <20210422120459.447350175@infradead.org> <20210422123308.196692074@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 23, 2021 at 06:22:52PM -0700, Josh Don wrote: > Hi Peter, > > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -186,12 +186,37 @@ int sysctl_sched_rt_runtime = 950000; > > > > void raw_spin_rq_lock_nested(struct rq *rq, int subclass) > > { > > - raw_spin_lock_nested(rq_lockp(rq), subclass); > > + raw_spinlock_t *lock; > > + > > + if (sched_core_disabled()) { > > Nothing to stop sched_core from being enabled right here? Leading to > us potentially taking the wrong lock. > > > + raw_spin_lock_nested(&rq->__lock, subclass); > > + return; > > + } > > + > > + for (;;) { > > + lock = rq_lockp(rq); > > + raw_spin_lock_nested(lock, subclass); > > + if (likely(lock == rq_lockp(rq))) > > + return; > > + raw_spin_unlock(lock); > > + } > > } Very good; something like the below seems to be the best I can make of it.. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f732642e3e09..1a81e9cc9e5d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -290,6 +290,10 @@ static void sched_core_assert_empty(void) static void __sched_core_enable(void) { static_branch_enable(&__sched_core_enabled); + /* + * Ensure raw_spin_rq_*lock*() have completed before flipping. + */ + synchronize_sched(); __sched_core_flip(true); sched_core_assert_empty(); } @@ -449,16 +453,22 @@ void raw_spin_rq_lock_nested(struct rq *rq, int subclass) { raw_spinlock_t *lock; + preempt_disable(); if (sched_core_disabled()) { raw_spin_lock_nested(&rq->__lock, subclass); + /* preempt *MUST* still be disabled here */ + preempt_enable_no_resched(); return; } for (;;) { lock = __rq_lockp(rq); raw_spin_lock_nested(lock, subclass); - if (likely(lock == __rq_lockp(rq))) + if (likely(lock == __rq_lockp(rq))) { + /* preempt *MUST* still be disabled here */ + preempt_enable_no_resched(); return; + } raw_spin_unlock(lock); } } @@ -468,14 +478,20 @@ bool raw_spin_rq_trylock(struct rq *rq) raw_spinlock_t *lock; bool ret; - if (sched_core_disabled()) - return raw_spin_trylock(&rq->__lock); + preempt_disable(); + if (sched_core_disabled()) { + ret = raw_spin_trylock(&rq->__lock); + preempt_enable(); + return ret; + } for (;;) { lock = __rq_lockp(rq); ret = raw_spin_trylock(lock); - if (!ret || (likely(lock == __rq_lockp(rq)))) + if (!ret || (likely(lock == __rq_lockp(rq)))) { + preempt_enable(); return ret; + } raw_spin_unlock(lock); } }