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=-8.0 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 774F8C433ED for ; Wed, 12 May 2021 13:37:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A982613D6 for ; Wed, 12 May 2021 13:37:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230301AbhELNiK (ORCPT ); Wed, 12 May 2021 09:38:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:30466 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230145AbhELNiD (ORCPT ); Wed, 12 May 2021 09:38:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620826615; 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=XL3YpNlHtEPSflvTqytFUav5pzWuom2+/jGcpkZ04jo=; b=OTfWX5f9GBkRzdoAiNkvva1ckwG4sO+QkBmpEbufROtW8EZjeelBdCbWPtpppVb4jzPk63 nZuzeKN1lri9bhD5Evduee3eVhVNktB5iumxk6UWTZUzLCf68KnLtY49FYxDJC7hGzgqY3 HqojyUZz1p7xtE+sp4eWtWh6SKcHodI= 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-113-o9Fy3_itMtaRfe0sG2Qh3w-1; Wed, 12 May 2021 09:36:52 -0400 X-MC-Unique: o9Fy3_itMtaRfe0sG2Qh3w-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E4D978B44DE; Wed, 12 May 2021 13:36:23 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.193.76]) by smtp.corp.redhat.com (Postfix) with SMTP id 2812D19CB0; Wed, 12 May 2021 13:36:18 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 12 May 2021 15:36:23 +0200 (CEST) Date: Wed, 12 May 2021 15:36:16 +0200 From: Oleg Nesterov To: Linus Torvalds Cc: Andrew Morton , "Eric W. Biederman" , Eugene Syromiatnikov , Jan Kratochvil , Mathieu Desnoyers , Michael Kerrisk , Pedro Alves , Simon Marchi , Linux Kernel Mailing List Subject: Re: [PATCH RESEND2] ptrace: make ptrace() fail if the tracee changed its pid unexpectedly Message-ID: <20210512133615.GA19594@redhat.com> References: <20210511165626.GA13720@redhat.com> <20210511175341.GA14488@redhat.com> <20210511180627.GB14488@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210511180627.GB14488@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/11, Oleg Nesterov wrote: > > On 05/11, Oleg Nesterov wrote: > > > > On 05/11, Linus Torvalds wrote: > > > > > That said, why this: > > > > > > > + rcu_read_lock(); > > > > + pid = task_pid_nr_ns(task, task_active_pid_ns(task->parent)); > > > > + rcu_read_unlock(); > > > > > > I don't see why the RCU read lock would be needed? task_pid_nr_ns() > > > does any required locking itself, afaik. > > > > > > And even if it wasn't, this all happens with siglock held, can > > > anything actually change. > > > > ... and with tasklist_lock held. > > > > Hmm. Linus, I am shy to admit I can't answer immediately, I'll recheck > > tomorrow after sleep. But it seems you are right. > > most probably to protect task->parent, not sure, this was 6 month ago... > but in this case we can use "current". I'll recheck. Of course you are right, rcu_read_lock() is not needed. Plus we can use task_pid_vnr() rather than task_pid_nr_ns(). I've sent v2. Thanks again, Oleg.