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=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 77545C2D0E4 for ; Tue, 17 Nov 2020 15:38:22 +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 D36502222C for ; Tue, 17 Nov 2020 15:38:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="1TRRyEOE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D36502222C 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:Date:In-reply-to:Message-ID: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=TQy7sKFrq6z6WwGWcpwVs6IauEFEnA6zIlCxJCpXDMo=; b=1TRRyEOERkJaYnMOZNj3T47cf xV/ZwO7qJjQF8WwFMt/AgMWg26s8ovnbw6cUBFldrSqyqHZ0KWX+0s498BOKoGDiOJPPrdEgUh0Ae Hx4P6TEZSW5Ul8S8Zi+qSDMiQadLnyKkl07XVxSJcOGJEU2mOPF1u2Ns9BCaxpLCQDM9haYv1JxjS +qnxaMyJUgdfOcO7NrJMUE9ZT+EnKj16Fb26chOTI6vk0N8kyqrbhs7tIDPnrYPN2AucbcmadZph0 CgBygMzY5Z9pW2ILjae+8IzqvBpnLtdPvsYnMDzjHvADAZAEe/skyKIfVJFYaO4ClPIk9WUCY0H2u cOVdKtc/w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kf333-00047d-7X; Tue, 17 Nov 2020 15:37:37 +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 1kf331-00046W-8u for linux-arm-kernel@lists.infradead.org; Tue, 17 Nov 2020 15:37:36 +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 B5F0BD6E; Tue, 17 Nov 2020 07:37:32 -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 B948E3F718; Tue, 17 Nov 2020 07:37:31 -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 Message-ID: In-reply-to: Date: Tue, 17 Nov 2020 15:37:24 +0000 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201117_103735_413118_1A5F4CBA X-CRM114-Status: GOOD ( 14.50 ) 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 12:52, Valentin Schneider wrote: > 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"? smp_acquire__after_ctrl_dep() that is, since we need ->on_rq load => 'current' bits load + store > 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 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=-8.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 79F82C5519F for ; Tue, 17 Nov 2020 15:37:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A6E52463C for ; Tue, 17 Nov 2020 15:37:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726298AbgKQPhe (ORCPT ); Tue, 17 Nov 2020 10:37:34 -0500 Received: from foss.arm.com ([217.140.110.172]:60078 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725790AbgKQPhd (ORCPT ); Tue, 17 Nov 2020 10:37:33 -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 B5F0BD6E; Tue, 17 Nov 2020 07:37:32 -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 B948E3F718; Tue, 17 Nov 2020 07:37:31 -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 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 Message-ID: In-reply-to: Date: Tue, 17 Nov 2020 15:37:24 +0000 MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/11/20 12:52, Valentin Schneider wrote: > 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"? smp_acquire__after_ctrl_dep() that is, since we need ->on_rq load => 'current' bits load + store > 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;