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=ham 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 8E6C4C282DA for ; Wed, 17 Apr 2019 15:21:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5851A20821 for ; Wed, 17 Apr 2019 15:21:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732631AbfDQPVO (ORCPT ); Wed, 17 Apr 2019 11:21:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58200 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729356AbfDQPVO (ORCPT ); Wed, 17 Apr 2019 11:21:14 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1700630016F2; Wed, 17 Apr 2019 15:21:06 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.38]) by smtp.corp.redhat.com (Postfix) with SMTP id 9D2855C207; Wed, 17 Apr 2019 15:20:56 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 17 Apr 2019 17:21:05 +0200 (CEST) Date: Wed, 17 Apr 2019 17:20:55 +0200 From: Oleg Nesterov To: Christian Brauner Cc: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, jannh@google.com, dhowells@redhat.com, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, serge@hallyn.com, luto@kernel.org, arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org, tglx@linutronix.de, mtk.manpages@gmail.com, akpm@linux-foundation.org, cyphar@cyphar.com, joel@joelfernandes.org, dancol@google.com Subject: Re: [PATCH v1 3/4] signal: support CLONE_PIDFD with pidfd_send_signal Message-ID: <20190417152055.GJ32622@redhat.com> References: <20190416170233.10208-1-christian@brauner.io> <20190416170233.10208-4-christian@brauner.io> <20190417140106.GG32622@redhat.com> <20190417141144.k2kmg7hd7pdpywyw@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190417141144.k2kmg7hd7pdpywyw@brauner.io> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Wed, 17 Apr 2019 15:21:14 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/17, Christian Brauner wrote: > > On Wed, Apr 17, 2019 at 04:01:06PM +0200, Oleg Nesterov wrote: > > On 04/16, Christian Brauner wrote: > > > > > > @@ -3581,12 +3588,12 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, > > > if (flags) > > > return -EINVAL; > > > > > > - f = fdget_raw(pidfd); > > > + f = fdget(pidfd); > > > > could you explain this change? > > > > I am just curious, I don't understand why should we disallow O_PATH and how > > this connects to this patch. > > Sending a signal through a pidfd is considered to be on a par with a > "write" to that pidfd. OK, but how this connects to "support pidfds" ? > Additionally, we use the fops associated with the fd to detect whether > it is actually a pidfd or not. This is not possible with O_PATH since > f_ops will be set to dummy fops. indeed... I didn't know this, thanks! But this means that pidfd_send_signal() will return -EBADF with or without this change; pidfd_to_pid() will return -EBADF even if fdget_raw() suceeds, right? To clarify, I am not arguing. I am trying to understand why exactly do we need this s/fdget_raw/fdget/ change and, why it doesn't come as a separate patch. Can you add a note into the changelog? Oleg.