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=-2.3 required=3.0 tests=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 6853AC32753 for ; Wed, 14 Aug 2019 16:34:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44C702133F for ; Wed, 14 Aug 2019 16:34:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728191AbfHNQer (ORCPT ); Wed, 14 Aug 2019 12:34:47 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:44056 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726509AbfHNQer (ORCPT ); Wed, 14 Aug 2019 12:34:47 -0400 Received: from [213.220.153.21] (helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.76) (envelope-from ) id 1hxwEX-000093-Ic; Wed, 14 Aug 2019 16:34:45 +0000 Date: Wed, 14 Aug 2019 18:34:44 +0200 From: Christian Brauner To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, libc-alpha@sourceware.org, alistair23@gmail.com, ebiederm@xmission.com, arnd@arndb.de, dalias@libc.org, torvalds@linux-foundation.org, adhemerval.zanella@linaro.org, fweimer@redhat.com, palmer@sifive.com, macro@wdc.com, zongbox@gmail.com, akpm@linux-foundation.org, viro@zeniv.linux.org.uk, hpa@zytor.com Subject: Re: [PATCH v3 1/1] waitid: Add support for waiting for the current process group Message-ID: <20190814163443.6odsksff4jbta7be@wittgenstein> References: <20190814154400.6371-1-christian.brauner@ubuntu.com> <20190814154400.6371-2-christian.brauner@ubuntu.com> <20190814160917.GG11595@redhat.com> <20190814161517.ldbn62mulk2pmqo5@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190814161517.ldbn62mulk2pmqo5@wittgenstein> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 14, 2019 at 06:15:17PM +0200, Christian Brauner wrote: > On Wed, Aug 14, 2019 at 06:09:17PM +0200, Oleg Nesterov wrote: > > On 08/14, Christian Brauner wrote: > > > > > > and a signal could come in between the system call that > > > retrieved the process gorup and the call to waitid that changes the > > ^^^^^ > > > current process group. > > > > I noticed this typo only because I spent 2 minutes or more trying to > > understand this sentence ;) But yes, a signal handler or another thread > > I'll try to rewrite it. :) Ok, here's what I changed it to: It was recently discovered that the linux version of waitid is not a superset of the other wait functions because it does not include support for waiting for the current process group. This has two downsides: 1. An extra system call is needed to get the current process group. 2. After the current process group is received and before it is passed to waitid a signal could arrive causing the current process group to change. Christian