Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751177AbdHXAmH (ORCPT ); Wed, 23 Aug 2017 20:42:07 -0400 Received: from mail-oi0-f65.google.com ([209.85.218.65]:34943 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751094AbdHXAmG (ORCPT ); Wed, 23 Aug 2017 20:42:06 -0400 MIME-Version: 1.0 In-Reply-To: <20170824022436.44adb497@mir> References: <20170816171211.4021-1-christian.brauner@ubuntu.com> <20170816194805.hnof3aqiqykwki7p@gmail.com> <87pobvruzt.fsf@xmission.com> <87ziazqdfr.fsf@xmission.com> <20170824022436.44adb497@mir> From: Linus Torvalds Date: Wed, 23 Aug 2017 17:42:05 -0700 X-Google-Sender-Auth: fuTinC71Z27U4EqpxUD8bRX3Yms Message-ID: Subject: Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name To: Stefan Lippers-Hollmann Cc: "Eric W. Biederman" , Christian Brauner , Christian Brauner , Linux Kernel Mailing List , "Serge E. Hallyn" , Al Viro , Thorsten Leemhuis Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1367 Lines: 35 On Wed, Aug 23, 2017 at 5:24 PM, Stefan Lippers-Hollmann wrote: > > This patch[1] as part of 4.13-rc6 (up to, at least, > v4.13-rc6-45-g6470812e2226) introduces a regression for me when using > pbuilder 0.228.7[2] (a helper to build Debian packages in a chroot and > to create and update its chroots) when trying to umount /dev/ptmx (inside > the chroot) on Debian/ unstable (full log and pbuilder configuration > file[3] attached). > > [...] > Setting up build-essential (12.3) ... > Processing triggers for libc-bin (2.24-15) ... > I: unmounting dev/ptmx filesystem > W: Could not unmount dev/ptmx: umount: /var/cache/pbuilder/build/1340/dev/ptmx: target is busy Yes, that patch definitely keeps a reference to the pts filesystem around while a pty is open. We always used to do that, but we did it differently - we would keep the 's_active' count elevated so that the superblock never went away, even after it was unmounted. Now it does an actual mntget(), and that makes umount _notice_ that the filesystem is still busy. How annoying. Because in a very real sehse the filesystem really is busy, but we used to hide it (perhaps on purpose - it's possible that people hit this problem before). Let me try to think about alteratives. Clearly this is a regression and I need to fix it, I just need to figure out _how_. Linus