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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 564FDC433F5 for ; Mon, 14 Mar 2022 18:54:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239013AbiCNSzx (ORCPT ); Mon, 14 Mar 2022 14:55:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58862 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232144AbiCNSzv (ORCPT ); Mon, 14 Mar 2022 14:55:51 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 5E6A52BCB for ; Mon, 14 Mar 2022 11:54:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647284079; 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=083jRPkrJnazoldsVs/TbU+MAEvPQEZLpxozIjfMarE=; b=MKSCRmivDljhrn+G32d8V4dLnnYX/DOhD9H1dLFGb1hZlArDtpcjok9+neqGZbyjNveXhP D18rmyYVxCLyqoArM5H+mA0cOZhwxeI9CsapSpOuzO5hB8aR0YxpGoExod9myqreMJIVqB VVw3PL2iFrlRr2CzdsxXNPTJmROjMwg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-493-AkQ1P6_VOLu2q2m4DjOOtg-1; Mon, 14 Mar 2022 14:54:36 -0400 X-MC-Unique: AkQ1P6_VOLu2q2m4DjOOtg-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 74D0318A6586; Mon, 14 Mar 2022 18:54:35 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.84]) by smtp.corp.redhat.com (Postfix) with SMTP id B5B53492C14; Mon, 14 Mar 2022 18:54:32 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 14 Mar 2022 19:54:33 +0100 (CET) Date: Mon, 14 Mar 2022 19:54:30 +0100 From: Oleg Nesterov To: Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, Ben Segall , Daniel Bristot de Oliveira , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Mel Gorman , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Vincent Guittot Subject: Re: [PATCH] ptrace: fix ptrace vs tasklist_lock race on PREEMPT_RT. Message-ID: <20220314185429.GA30364@redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I never really understood ->saved_state logic. Will read this patch tomorrow, but at first glance this patch doesn't solve all problems. On 03/02, Sebastian Andrzej Siewior wrote: > > +static inline bool __task_state_match_eq(struct task_struct *tsk, long state) > +{ > + bool match = false; > + > + if (READ_ONCE(tsk->__state) == state) > + match = true; > + else if (tsk->saved_state == state) > + match = true; > + return match; > +} ... > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3239,7 +3239,8 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state > * is actually now running somewhere else! > */ > while (task_running(rq, p)) { > - if (match_state && unlikely(READ_ONCE(p->__state) != match_state)) > + if (match_state && > + unlikely(!task_state_match_eq(p, match_state))) > return 0; So wait_task_inactive() can return 0 but the task can run after that, right? This is not what we want... Oleg.