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 30B69C63697 for ; Tue, 17 Nov 2020 19:32:51 +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 BB51B24248 for ; Tue, 17 Nov 2020 19:32:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="MXQ+Buja" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB51B24248 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com 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:MIME-Version:Message-ID:Date:In-reply-to:Subject:To: From:References:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=KtmO2p52IMWhYuyjrrFu5I5xppmsM8oCoUJB01GCDEI=; b=MXQ+BujagSJwfkvV5Vs+qOA1d cumXAGT3B6d/y6tjM8qMxe6aIsyjpElT6TKUAKXyGC00n2WXGOwzf3Ni7F4zvOsfYv9HpLjv0SwAT zkqF+Vq9Qs7wcwzmPztrC9C56zvjfb963viGQr3W0fg3zCWA6Tfe6sUQE5TbTl/3//xtHhw26GvEB Rps4WSfU7ULjLu7jXUeJ4qWQ+oCzx4BBC8hmtQUBPjfBOMa9Op5DYyjydb8+rvfuiRgdgYNidrv21 QDjr9mUIQJC3KdTACb7hVMbrHBhkDSh37FadWCu+Eb5XIhjc/86H084uqAYf7Zz+STMCNC8CtsSH/ ZlzzS+mgQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kf6iF-0000c6-J4; Tue, 17 Nov 2020 19:32:23 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kf6iD-0000bd-F9 for linux-arm-kernel@lists.infradead.org; Tue, 17 Nov 2020 19:32:22 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1F899101E; Tue, 17 Nov 2020 11:32:20 -0800 (PST) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 348B93F718; Tue, 17 Nov 2020 11:32:19 -0800 (PST) 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> <20201117161318.GP3121392@hirez.programming.kicks-ass.net> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Peter Zijlstra Subject: Re: [PATCH] sched: Fix data-race in wakeup In-reply-to: <20201117161318.GP3121392@hirez.programming.kicks-ass.net> Date: Tue, 17 Nov 2020 19:32:16 +0000 Message-ID: MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201117_143221_557964_6B07577F X-CRM114-Status: GOOD ( 13.88 ) 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 17/11/20 16:13, Peter Zijlstra wrote: > 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. Apologies for the messy train of thought; what I was trying to say is that we have already the following, which AIUI is sufficient: * p->XXX = X; ttwu() * schedule() if (p->on_rq && ..) // false * smp_mb__after_spinlock(); smp_acquire__after_ctrl_dep(); * deactivate_task() ttwu_queue_wakelist() * p->on_rq = 0; p->sched_remote_wakeup = Y; _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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, 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 C5354C2D0E4 for ; Tue, 17 Nov 2020 19:32:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8492524698 for ; Tue, 17 Nov 2020 19:32:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729195AbgKQTcV (ORCPT ); Tue, 17 Nov 2020 14:32:21 -0500 Received: from foss.arm.com ([217.140.110.172]:35518 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726035AbgKQTcU (ORCPT ); Tue, 17 Nov 2020 14:32:20 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1F899101E; Tue, 17 Nov 2020 11:32:20 -0800 (PST) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 348B93F718; Tue, 17 Nov 2020 11:32:19 -0800 (PST) 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> <20201117161318.GP3121392@hirez.programming.kicks-ass.net> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Peter Zijlstra Cc: Will Deacon , Mel Gorman , Davidlohr Bueso , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: Fix data-race in wakeup In-reply-to: <20201117161318.GP3121392@hirez.programming.kicks-ass.net> Date: Tue, 17 Nov 2020 19:32:16 +0000 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/11/20 16:13, Peter Zijlstra wrote: > 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. Apologies for the messy train of thought; what I was trying to say is that we have already the following, which AIUI is sufficient: * p->XXX = X; ttwu() * schedule() if (p->on_rq && ..) // false * smp_mb__after_spinlock(); smp_acquire__after_ctrl_dep(); * deactivate_task() ttwu_queue_wakelist() * p->on_rq = 0; p->sched_remote_wakeup = Y;