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=-2.2 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 71DDCC7618B for ; Thu, 25 Jul 2019 11:44:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DB2622CBD for ; Thu, 25 Jul 2019 11:44:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404226AbfGYLoP (ORCPT ); Thu, 25 Jul 2019 07:44:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45212 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388154AbfGYLoM (ORCPT ); Thu, 25 Jul 2019 07:44:12 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 92FC37BEE3; Thu, 25 Jul 2019 11:44:03 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 34D3A60BEC; Thu, 25 Jul 2019 11:44:00 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 25 Jul 2019 13:44:03 +0200 (CEST) Date: Thu, 25 Jul 2019 13:43:59 +0200 From: Oleg Nesterov To: Christian Brauner Cc: linux-kernel@vger.kernel.org, arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org, joel@joelfernandes.org, tglx@linutronix.de, tj@kernel.org, dhowells@redhat.com, jannh@google.com, luto@kernel.org, akpm@linux-foundation.org, cyphar@cyphar.com, torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, kernel-team@android.com, Ingo Molnar , Peter Zijlstra , linux-api@vger.kernel.org Subject: Re: [PATCH 4/5] pidfd: add CLONE_WAIT_PID Message-ID: <20190725114359.GH4707@redhat.com> References: <20190724144651.28272-1-christian@brauner.io> <20190724144651.28272-5-christian@brauner.io> <20190725103543.GF4707@redhat.com> <20190725104006.7myahvjtnbcgu3in@brauner.io> <20190725112503.GG4707@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190725112503.GG4707@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 25 Jul 2019 11:44:11 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Or. We can change wait_consider_task() to not clear ->notask_error if WXXX and the child is PF_WAIT_PID. This way you can "safely" use wait() without WNOHANG, it won't block if all the children which can report an even are PF_WAIT_PID. But I do not understand your use-cases, I have no idea if this can help or not. Just I think the more discussion is always better when we are going to add the new API. On 07/25, Oleg Nesterov wrote: > > On 07/25, Christian Brauner wrote: > > > > On Thu, Jul 25, 2019 at 12:35:44PM +0200, Oleg Nesterov wrote: > > > > > > I have to admit this feature looks a bit exotic to me... > > > > It might look like it from the kernels perspective but from the feedback > > on this when presenting on this userspace has real usecases for this. > > OK... > > but then perhaps we can make PF_WAIT_PID more flexible. > > Say, we can add the new WXXX wait option and change eligible_child() > > if ((p->flags & PF_WAIT_PID) && (wo->options & WXXX)) > return 0; > > this way the parent can tell waitid() whether the PF_WAIT_PID tasks should > be filtered or not. > > And if we do this we can even add PR_SET_WAIT_PID/PR_CLR_WAIT_PID instead > of the new CLONE_ flag. > > Oleg.