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 96637C433EF for ; Thu, 28 Apr 2022 11:19:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345506AbiD1LWp (ORCPT ); Thu, 28 Apr 2022 07:22:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345190AbiD1LWo (ORCPT ); Thu, 28 Apr 2022 07:22:44 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A0AE3A94E7 for ; Thu, 28 Apr 2022 04:19:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651144769; 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=Qr2DOGB0z6K0qePNKw8JJPlRt9jZnLNpgbFm3MJ8HzE=; b=eNKVgpbvjOSnx86OScTqbuZpid+U+vejq4zFJTjH0smxRRL+mTTkBGmqPkfl77+KfMAvI9 VFKhWaLgnZicHcYoaC9/SlNuqNMB0kfmNExnHU6M/q9dWl5AhH3/TiMpTw0aqfAT2PZLS/ hjqts5K8zKjZNx30sP3KAJtsUfREpN8= 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-416-PeK0j-6rMlibt-Yq8wehuw-1; Thu, 28 Apr 2022 07:19:24 -0400 X-MC-Unique: PeK0j-6rMlibt-Yq8wehuw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CD7BE1815CFC; Thu, 28 Apr 2022 11:19:17 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.193.96]) by smtp.corp.redhat.com (Postfix) with SMTP id C6B052166B18; Thu, 28 Apr 2022 11:19:12 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 28 Apr 2022 13:19:17 +0200 (CEST) Date: Thu, 28 Apr 2022 13:19:11 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: "Eric W. Biederman" , linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , inux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn Subject: Re: [PATCH 7/9] ptrace: Simplify the wait_task_inactive call in ptrace_check_attach Message-ID: <20220428111911.GA3804@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-7-ebiederm@xmission.com> <20220427151455.GE17421@redhat.com> 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 2.78 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 04/28, Peter Zijlstra wrote: > > On Wed, Apr 27, 2022 at 05:14:57PM +0200, Oleg Nesterov wrote: > > On 04/26, Eric W. Biederman wrote: > > > > > > Asking wait_task_inactive to verify that tsk->__state == __TASK_TRACED > > > was needed to detect the when ptrace_stop would decide not to stop > > > after calling "set_special_state(TASK_TRACED)". With the recent > > > cleanups ptrace_stop will always stop after calling set_special_state. > > > > > > Take advatnage of this by no longer asking wait_task_inactive to > > > verify the state. If a bug is hit and wait_task_inactive does not > > > succeed warn and return -ESRCH. > > > > ACK, but I think that the changelog is wrong. > > > > We could do this right after may_ptrace_stop() has gone. This doesn't > > depend on the previous changes in this series. > > It very much does rely on there not being any blocking between > set_special_state() and schedule() tho. So all those PREEMPT_RT > spinlock->rt_mutex things need to be gone. Yes sure. But this patch doesn't add the new problems, imo. Yes we can hit the WARN_ON_ONCE(!wait_task_inactive()), but this is correct in that it should not fail, and this is what we need to fix. > That is also the reason I couldn't do wait_task_inactive(task, 0) Ah, I din't notice this patch uses wait_task_inactive(child, 0), I think it should do wait_task_inactive(child, __TASK_TRACED). Oleg.