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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 9538BC433DF for ; Tue, 21 Jul 2020 15:38:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7364F20771 for ; Tue, 21 Jul 2020 15:38:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="INEZPk0w" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730066AbgGUPig (ORCPT ); Tue, 21 Jul 2020 11:38:36 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:46045 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726654AbgGUPif (ORCPT ); Tue, 21 Jul 2020 11:38:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595345914; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=25NJ3yo8pL9dVKE37MGLGkTary9Phb3OtmX8VRE0Cvc=; b=INEZPk0wMJHTKUlZ3JE/onN1qAAMhff7d/NtiSGzg9Ose0gwECLTy1LLIgdZsqLjObFblp A1/1NL7WTDyU5PWQQY5eilCerJy//Eb3Rl2/jej1lT2pONX2ZoF2RwFlEkaJ+sgOIDoFPK S97PQ9fPLwxTMnlecY/5CP28MIwQJIY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-145-yqrVKZXmMyWcalF69rgd7Q-1; Tue, 21 Jul 2020 11:38:30 -0400 X-MC-Unique: yqrVKZXmMyWcalF69rgd7Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 535981083E81; Tue, 21 Jul 2020 15:38:28 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.225]) by smtp.corp.redhat.com (Postfix) with SMTP id 54DD02B4DB; Tue, 21 Jul 2020 15:38:25 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 21 Jul 2020 17:38:28 +0200 (CEST) Date: Tue, 21 Jul 2020 17:38:24 +0200 From: Oleg Nesterov To: peterz@infradead.org Cc: Paul Gortmaker , Jiri Slaby , Christian Brauner , christian@brauner.io, "Eric W. Biederman" , Linux kernel mailing list , Mel Gorman , Dave Jones Subject: Re: [PATCH] sched: Fix race against ptrace_freeze_trace() Message-ID: <20200721153823.GA28364@redhat.com> References: <20200720064326.GA6612@redhat.com> <20200720082657.GC6612@redhat.com> <20200720084106.GJ10769@hirez.programming.kicks-ass.net> <20200720105924.GE43129@hirez.programming.kicks-ass.net> <20200720140224.GD6612@redhat.com> <20200720142105.GR10769@hirez.programming.kicks-ass.net> <20200721045251.GA28481@windriver.com> <20200721083753.GH119549@hirez.programming.kicks-ass.net> <20200721121308.GH43129@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200721121308.GH43129@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/21, Peter Zijlstra wrote: > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4193,9 +4193,6 @@ static void __sched notrace __schedule(b > local_irq_disable(); > rcu_note_context_switch(preempt); > > - /* See deactivate_task() below. */ > - prev_state = prev->state; > - > /* > * Make sure that signal_pending_state()->signal_pending() below > * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE) > @@ -4219,11 +4216,16 @@ static void __sched notrace __schedule(b > update_rq_clock(rq); > > switch_count = &prev->nivcsw; > + > /* > - * We must re-load prev->state in case ttwu_remote() changed it > - * before we acquired rq->lock. > + * We must load prev->state once (task_struct::state is volatile), such > + * that: > + * > + * - we form a control dependency vs deactivate_task() below. > + * - ptrace_{,un}freeze_traced() can change ->state underneath us. > */ > - if (!preempt && prev_state && prev_state == prev->state) { > + prev_state = prev->state; > + if (!preempt && prev_state) { Thanks! FWIW, Acked-by: Oleg Nesterov