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 2ABDBC2D0E4 for ; Tue, 17 Nov 2020 12:52:52 +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 A3C2A2222E for ; Tue, 17 Nov 2020 12:52:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="qOhM4P5/" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A3C2A2222E 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=7dz5zEWZmH1qvB1oWsgYT4rAm8welaeDkXxmkeBaiJc=; b=qOhM4P5/k01TYJlkkjfk+xobt xX3C60kogCiNO6lrlV5TmVjLlK5tNnCmtEEuZUI/BffrWzeD1RHcATez2jH7wJcAgOJALixYMoYtZ sOw+E2cJ7tGtBLOW8E/ru2C9PpkAcFJ3kbPpGpBQR/fFr2nyKbdusp7HeztoXffAlRv0e5DHifhWO s4/73o80vCSbK5ripru/rcU8IZArIEu55oNL/xMIQteKJkOeMt3ONR20LFbaB5vM5bMRz8hA6lfDc lKXWuZt7xn9NNkpn61pvlA+ikVOI7skzbJZA1ksINreByjyNh2osjuQQmypgv0Y9OVHt5/3HRDGgC +//nl1DLw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kf0T6-00089X-Tg; Tue, 17 Nov 2020 12:52:20 +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 1kf0T4-000885-1w for linux-arm-kernel@lists.infradead.org; Tue, 17 Nov 2020 12:52:19 +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 989AC101E; Tue, 17 Nov 2020 04:52:15 -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 B29AF3F719; Tue, 17 Nov 2020 04:52:14 -0800 (PST) References: <20201116091054.GL3371@techsingularity.net> <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> 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: <20201117094621.GE3121429@hirez.programming.kicks-ass.net> Date: Tue, 17 Nov 2020 12:52:12 +0000 Message-ID: MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201117_075218_184471_13A53C6B X-CRM114-Status: GOOD ( 15.01 ) 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 09:46, Peter Zijlstra wrote: > How's this then? It still doesn't explicitly call out the specific race, > but does mention the more fundamental issue that wakelist queueing > doesn't respect the regular rules anymore. > > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -775,7 +775,6 @@ struct task_struct { > unsigned sched_reset_on_fork:1; > unsigned sched_contributes_to_load:1; > unsigned sched_migrated:1; > - unsigned sched_remote_wakeup:1; > #ifdef CONFIG_PSI > unsigned sched_psi_wake_requeue:1; > #endif > @@ -785,6 +784,21 @@ struct task_struct { > > /* Unserialized, strictly 'current' */ > > + /* > + * 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"? That should be giving the right ordering for the rest of ttwu() wrt. those 'current' bits, considering they are written before that smp_mb__after_spinlock(). In any case, consider me convinced: Reviewed-by: Valentin Schneider > + unsigned sched_remote_wakeup:1; > + > /* Bit to tell LSMs we're in execve(): */ > unsigned in_execve:1; > unsigned in_iowait:1; _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel