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_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 F1C7BC433E0 for ; Tue, 30 Jun 2020 13:22:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0F99206C0 for ; Tue, 30 Jun 2020 13:22:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730070AbgF3NWX (ORCPT ); Tue, 30 Jun 2020 09:22:23 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:53064 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726012AbgF3NWX (ORCPT ); Tue, 30 Jun 2020 09:22:23 -0400 Received: from fsav405.sakura.ne.jp (fsav405.sakura.ne.jp [133.242.250.104]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 05UDLOlk013584; Tue, 30 Jun 2020 22:21:24 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav405.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav405.sakura.ne.jp); Tue, 30 Jun 2020 22:21:24 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav405.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 05UDLNN3013564 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 30 Jun 2020 22:21:23 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH v2 00/15] Make the user mode driver code a better citizen To: "Eric W. Biederman" , Alexei Starovoitov Cc: linux-kernel@vger.kernel.org, David Miller , Greg Kroah-Hartman , Kees Cook , Andrew Morton , Alexei Starovoitov , Al Viro , bpf , linux-fsdevel , Daniel Borkmann , Jakub Kicinski , Masahiro Yamada , Gary Lin , Bruno Meneguele , LSM List , Casey Schaufler , Luis Chamberlain , Linus Torvalds References: <20200625095725.GA3303921@kroah.com> <778297d2-512a-8361-cf05-42d9379e6977@i-love.sakura.ne.jp> <20200625120725.GA3493334@kroah.com> <20200625.123437.2219826613137938086.davem@davemloft.net> <87pn9mgfc2.fsf_-_@x220.int.ebiederm.org> <87y2oac50p.fsf@x220.int.ebiederm.org> <87bll17ili.fsf_-_@x220.int.ebiederm.org> <20200629221231.jjc2czk3ul2roxkw@ast-mbp.dhcp.thefacebook.com> <87eepwzqhd.fsf@x220.int.ebiederm.org> From: Tetsuo Handa Message-ID: <1f4d8b7e-bcff-f950-7dac-76e3c4a65661@i-love.sakura.ne.jp> Date: Tue, 30 Jun 2020 22:21:19 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <87eepwzqhd.fsf@x220.int.ebiederm.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/06/30 21:29, Eric W. Biederman wrote: > Hmm. The wake up happens just of tgid->wait_pidfd happens just before > release_task is called so there is a race. As it is possible to wake > up and then go back to sleep before pid_has_task becomes false. What is the reason we want to wait until pid_has_task() becomes false? - wait_event(tgid->wait_pidfd, !pid_has_task(tgid, PIDTYPE_TGID)); + while (!wait_event_timeout(tgid->wait_pidfd, !pid_has_task(tgid, PIDTYPE_TGID), 1)); By the way, commit 4a9d4b024a3102fc ("switch fput to task_work_add") says that use of flush_delayed_fput() has to be careful. Al, is it safe to call flush_delayed_fput() from blob_to_mnt() from umd_load_blob() (which might be called from both kernel thread and from process context (e.g. init_module() syscall by /sbin/insmod )) ?