From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: util-linux-owner@vger.kernel.org Received: from mx1.redhat.com ([209.132.183.28]:57065 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751109AbaICHpW (ORCPT ); Wed, 3 Sep 2014 03:45:22 -0400 Date: Wed, 3 Sep 2014 09:45:17 +0200 From: Karel Zak To: Stanislav Brabec Cc: util-linux@vger.kernel.org Subject: Re: umount of unreachable NFS without -f [maybe PATCH] Message-ID: <20140903074517.GD21325@x2.net.home> References: <1409684978.14709.15.camel@oct.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1409684978.14709.15.camel@oct.suse.cz> Sender: util-linux-owner@vger.kernel.org List-ID: On Tue, Sep 02, 2014 at 09:09:38PM +0200, Stanislav Brabec wrote: > I just analyzed causes of hang while calling umount without -f on an > unreachable NFS. > > The first hang happens on in lookup_umount_fs(): > > stat(tgt, &st) == 0 && S_ISDIR(st.st_mode) > > I don't exactly know, what its removal causes, but I tried it. > > I entered into next hang in mnt_resolve_path() inside has_utab_entry(). > We cannot prevent this hang in all cases, but preventing it in a > standard situation is pretty straightforward: Try to match provided > target name before trying to canonicalize. > > Now my umount without -f works well at least in the case, when the mount > point is recorded in the utab. > > If it is not recorded in utab, it still hangs later in > lookup_umount_fs() on: > > if (statfs(tgt, &vfs) == 0) > > Well, we can prevent even this hang, but it would be at cost of parsing > mtab. I read your git comments and I see, that the whole purpose of the > code is preventing of parsing of the generated mtab/mountinfo. > > Would be parsing of fstab a safe way without paying this cost? How often do you have NFS mounts without entry within utab? I think it's pretty unusual (I guess you have mount.nfs linked with libmount). The change in has_utab_entry() is definitely good idea, but I'm not sure about the rest. Maybe it would be enough to call has_utab_entry() before stat(tgt, &st) == 0 && S_ISDIR(st.st_mode) then it will be good enough for almost all NFS mounts (with utab entries). Karel -- Karel Zak http://karelzak.blogspot.com