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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 E3B24C4363D for ; Thu, 24 Sep 2020 12:30:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 80A9A221EB for ; Thu, 24 Sep 2020 12:30:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="hE6dPepO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727780AbgIXM3w (ORCPT ); Thu, 24 Sep 2020 08:29:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727561AbgIXM3u (ORCPT ); Thu, 24 Sep 2020 08:29:50 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EDE10C0613CE for ; Thu, 24 Sep 2020 05:29:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=wtQTDdmEMh1+PZHybPfpi61tawXPQ1boTfv/FGVLjNI=; b=hE6dPepONZJMY8VTlwfQ4l7JiJ 9vljV1Fwlfrr4y0G+z/26oXS8phHqllfuQjFumk75NFx5D15Cv0PcQIW+n+EUiYbx5m+WCpzPU2gu icYfowBARkDnWV0sHOFeHy2GkjaCXAUC76mirY2pfLJenUjUfc/KLkKnE5iVxYTyOWwDXGqL83tcd J2PgBZhXARsyTSUX68muDTXJZtTuFNTeB1d46dFmawJOss4TyqebiIAL+SPg6084VdrZSn5hUSM8X 0nxRRoxZAVQx6yzhU/NJOdYDdcoc7cYX1+niIIMqm3lfBAHj45UteLq+K8weEYMrAgv1qXO9N6DGq CKzNnZuA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLQNT-0006Cl-Ca; Thu, 24 Sep 2020 12:29:35 +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 A37383059DE; Thu, 24 Sep 2020 14:29:34 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8E08720315103; Thu, 24 Sep 2020 14:29:34 +0200 (CEST) Date: Thu, 24 Sep 2020 14:29:34 +0200 From: Peter Zijlstra To: Valentin Schneider Cc: tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, bigeasy@linutronix.de, qais.yousef@arm.com, swood@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vincent.donnefort@arm.com Subject: Re: [PATCH 7/9] sched: Add migrate_disable() Message-ID: <20200924122934.GI2628@hirez.programming.kicks-ass.net> References: <20200921163557.234036895@infradead.org> <20200921163845.769861942@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 Thu, Sep 24, 2020 at 12:53:25PM +0100, Valentin Schneider wrote: > On 21/09/20 17:36, Peter Zijlstra wrote: > > [...] > > > +void migrate_enable(void) > > +{ > > + if (--current->migration_disabled) > > + return; > > + > > + barrier(); > > + > > + if (p->cpus_ptr == &p->cpus_mask) > > + return; > > If we get to here this means we're the migrate_enable() invocation that > marks the end of the migration_disabled region. How can cpus_ptr already > point back to current's cpus_mask? It might never have been changed away. migrate_disable() ->migration_disabled++; | | | | | v | migrate_disable_switch() | if (->cpus_ptr == &->cpus_mask) | __do_set_cpus_allowed(.new_mask = cpumask_of()) | | | | v v migrate_enable() ->migration_disabled--; Only if we've passed through a context switch between migrate_disable() and migrate_enable() will the mask have been changed.