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=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 2DE3CC5519F for ; Tue, 17 Nov 2020 16:13:55 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 87B05221F8 for ; Tue, 17 Nov 2020 16:13:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="3P+/skNt" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87B05221F8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject: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=biDLav/DK9XNBNNCIQiKRptxjJpgLhLowdZHUy1KH2A=; b=3P+/skNtcxOLVN9uZXG7/x26p PYE9Z0GJGKQhSmP7q1GMVZ2ti5xUWn3l/rigm1OE2+enO9EyLjRPgT/WMgpR2hEwiNcWJYQRCupU8 LOSKwPUH2TUCXXxCKy3oKSkDYaSHxVccKYkBmNoEBv2NypCKwjXA3u4cSKvZgh01y3Z4bcTdTe+w5 HJhWfEglXse1hpSvFk/CIqGuH60obtVuXHYHodMPfpUIkilIwLHzuPjEGkLZ3AjjE6wo0o8XzLN2E O4KhZLiHHpGD+tY/Cx5APUTiVAmhqYp4BQRAAU2LYNifNGOIldz7y6J+B23O82q0qXeR/QmZik0ew 8N1p2cwHQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kf3bg-0008TB-D7; Tue, 17 Nov 2020 16:13:24 +0000 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 1kf3be-0008So-JC; Tue, 17 Nov 2020 16:13:22 +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 654883019CE; Tue, 17 Nov 2020 17:13:18 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 4F6C0203DEE9D; Tue, 17 Nov 2020 17:13:18 +0100 (CET) Date: Tue, 17 Nov 2020 17:13:18 +0100 From: Peter Zijlstra To: Valentin Schneider Subject: Re: [PATCH] sched: Fix data-race in wakeup Message-ID: <20201117161318.GP3121392@hirez.programming.kicks-ass.net> References: <20201116131102.GA29992@willie-the-truck> <20201116133721.GQ3371@techsingularity.net> <20201116142005.GE3121392@hirez.programming.kicks-ass.net> <20201116193149.GW3371@techsingularity.net> <20201117083016.GK3121392@hirez.programming.kicks-ass.net> <20201117091545.GA31837@willie-the-truck> <20201117092936.GA3121406@hirez.programming.kicks-ass.net> <20201117094621.GE3121429@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mel Gorman , Davidlohr Bueso , Will Deacon , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org 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 Tue, Nov 17, 2020 at 03:37:24PM +0000, Valentin Schneider wrote: > >> + /* > >> + * This field must not be in the scheduler word above due to wakelist > >> + * queueing no longer being serialized by p->on_cpu. However: > >> + * > >> + * p->XXX = X; ttwu() > >> + * schedule() if (p->on_rq && ..) // false > >> + * smp_mb__after_spinlock(); if (smp_load_acquire(&p->on_cpu) && //true > >> + * deactivate_task() ttwu_queue_wakelist()) > >> + * p->on_rq = 0; p->sched_remote_wakeup = Y; > >> + * > >> + * guarantees all stores of 'current' are visible before > >> + * ->sched_remote_wakeup gets used, so it can be in this word. > >> + */ > > > > Isn't the control dep between that ttwu() p->on_rq read and > > p->sched_remote_wakeup write "sufficient"? > > smp_acquire__after_ctrl_dep() that is, since we need > ->on_rq load => 'current' bits load + store I don't think we need that extra barrier; after all, there will be a complete schedule() between waking the task and it actually becoming current. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel