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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 22634C04E53 for ; Wed, 15 May 2019 15:22:39 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 9FDDD20862 for ; Wed, 15 May 2019 15:22:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9FDDD20862 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 453ywX29cvzDqVf for ; Thu, 16 May 2019 01:22:36 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=redhat.com (client-ip=209.132.183.28; helo=mx1.redhat.com; envelope-from=oleg@redhat.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=redhat.com Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 453yrs2shGzDqP0 for ; Thu, 16 May 2019 01:19:25 +1000 (AEST) Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1942D301A3E1; Wed, 15 May 2019 15:19:22 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.159]) by smtp.corp.redhat.com (Postfix) with SMTP id AC9925D9C0; Wed, 15 May 2019 15:19:16 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 15 May 2019 17:19:19 +0200 (CEST) Date: Wed, 15 May 2019 17:19:13 +0200 From: Oleg Nesterov To: Christian Brauner Subject: Re: [PATCH 1/2] pid: add pidfd_open() Message-ID: <20190515151912.GE18892@redhat.com> References: <20190515100400.3450-1-christian@brauner.io> <20190515143857.GB18892@redhat.com> <20190515144927.f2yxyi6w6lhn3xx7@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190515144927.f2yxyi6w6lhn3xx7@brauner.io> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Wed, 15 May 2019 15:19:22 +0000 (UTC) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, linux-mips@vger.kernel.org, dhowells@redhat.com, linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org, linux-api@vger.kernel.org, elena.reshetova@intel.com, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, linux-xtensa@linux-xtensa.org, keescook@chromium.org, arnd@arndb.de, jannh@google.com, linux-m68k@lists.linux-m68k.org, viro@zeniv.linux.org.uk, luto@kernel.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, linux-parisc@vger.kernel.org, cyphar@cyphar.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, luto@amacapital.net, ebiederm@xmission.com, linux-alpha@vger.kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 05/15, Christian Brauner wrote: > > On Wed, May 15, 2019 at 04:38:58PM +0200, Oleg Nesterov wrote: > > > > it seems that you can do a single check > > > > tsk = pid_task(p, PIDTYPE_TGID); > > if (!tsk) > > ret = -ESRCH; > > > > this even looks more correct if we race with exec changing the leader. > > The logic here being that you can only reach the thread_group leader > from struct pid if PIDTYPE_PID == PIDTYPE_TGID for this struct pid? Not exactly... it is not that PIDTYPE_PID == PIDTYPE_TGID for this pid, struct pid has no "type" or something like this. The logic is that pid->tasks[PIDTYPE_XXX] is the list of task which use this pid as "XXX" type. For example, clone(CLONE_THREAD) creates a pid which has a single non- empty list, pid->tasks[PIDTYPE_PID]. This pid can't be used as TGID or SID. So if pid_task(PIDTYPE_TGID) returns non-NULL we know that this pid was used for a group-leader, see copy_process() which does if (thread_group_leader(p)) attach_pid(p, PIDTYPE_TGID); If we race with exec which changes the leader pid_task(TGID) can return the old leader. We do not care, but this means that we should not check thread_group_leader(). Oleg.