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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1ED3BC28CBC for ; Sat, 9 May 2020 20:01:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CFB120731 for ; Sat, 9 May 2020 20:01:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728648AbgEIUBM (ORCPT ); Sat, 9 May 2020 16:01:12 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:44674 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727938AbgEIUBM (ORCPT ); Sat, 9 May 2020 16:01:12 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jXVei-0004RB-KV; Sat, 09 May 2020 14:01:04 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jXVeh-0002GG-On; Sat, 09 May 2020 14:01:04 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Linus Torvalds Cc: Linux Kernel Mailing List , Oleg Nesterov , Jann Horn , Kees Cook , Greg Ungerer , Rob Landley , Bernd Edlinger , linux-fsdevel , Al Viro , Alexey Dobriyan , Andrew Morton References: <87h7wujhmz.fsf@x220.int.ebiederm.org> <87sgga6ze4.fsf@x220.int.ebiederm.org> <87blmy6zay.fsf_-_@x220.int.ebiederm.org> Date: Sat, 09 May 2020 14:57:33 -0500 In-Reply-To: (Linus Torvalds's message of "Sat, 9 May 2020 12:18:06 -0700") Message-ID: <87k11kyj82.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jXVeh-0002GG-On;;;mid=<87k11kyj82.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX199Tk+7UP647KCMuhUlT5KO3eF9VrjxQc8= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 3/6] exec: Stop open coding mutex_lock_killable of cred_guard_mutex X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Linus Torvalds writes: > On Fri, May 8, 2020 at 11:48 AM Eric W. Biederman wrote: >> >> >> Oleg modified the code that did >> "mutex_lock_interruptible(¤t->cred_guard_mutex)" to return >> -ERESTARTNOINTR instead of -EINTR, so that userspace will never see a >> failure to grab the mutex. >> >> Slightly earlier Liam R. Howlett defined mutex_lock_killable for >> exactly the same situation but it does it a little more cleanly. > > What what what? > > None of this makes sense. Your commit message is completely wrong, and > the patch is utter shite. > > mutex_lock_interruptible() and mutex_lock_killable() are completely > different operations, and the difference has absolutely nothing to do > with -ERESTARTNOINTR or -EINTR. > > mutex_lock_interruptible() is interrupted by any signal. > > mutex_lock_killable() is - surprise surprise - only interrupted by > SIGKILL (in theory any fatal signal, but we never actually implemented > that logic, so it's only interruptible by the known-to-always-be-fatal > SIGKILL). > >> Switch the code to mutex_lock_killable so that it is clearer what the >> code is doing. > > This nonsensical patch makes me worry about all your other patches. > The explanation is wrong, the patch is wrong, and it changes things to > be fundamentally broken. > > Before this, ^C would break out of a blocked execve()/ptrace() > situation. After this patch, you need special tools to do so. > > This patch is completely wrong. Sigh. Brain fart on my part. You are correct. I saw the restart, and totally forgot that it allows the handling of a signal before restarting the system call. Except for the handling of the signal in userspace it is the same as mutex_lock_killable but that is a big big big if. My apologies. I will drop this patch. Eric