From patchwork Mon Feb 18 02:25:09 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 2155001 Return-Path: X-Original-To: patchwork-linux-nfs@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id 2B48CDF283 for ; Mon, 18 Feb 2013 02:25:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757462Ab3BRCZ2 (ORCPT ); Sun, 17 Feb 2013 21:25:28 -0500 Received: from cantor2.suse.de ([195.135.220.15]:33953 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755687Ab3BRCZ1 (ORCPT ); Sun, 17 Feb 2013 21:25:27 -0500 Received: from relay1.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 436F3A3DDF; Mon, 18 Feb 2013 03:25:22 +0100 (CET) Date: Mon, 18 Feb 2013 13:25:09 +1100 From: NeilBrown To: Jeff Layton Cc: "Myklebust, Trond" , Alexander Viro , NFS Subject: Re: More fun with unmounting ESTALE directories. Message-ID: <20130218132509.0ce779de@notabene.brown> In-Reply-To: <20130214104230.013b7f71@tlielax.poochiereds.net> References: <20130212113813.427b8e05@notabene.brown> <20130214104230.013b7f71@tlielax.poochiereds.net> X-Mailer: Claws Mail 3.8.1 (GTK+ 2.24.10; x86_64-suse-linux-gnu) Mime-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Thu, 14 Feb 2013 10:42:30 -0500 Jeff Layton wrote: > On Tue, 12 Feb 2013 11:38:13 +1100 > NeilBrown wrote: > > > > > I've been exploring difficulties with unmounting stale directories and > > discovered another bug. > > > > If I: > > > > SERVER: mkdir /foo/bar #and make sure it is exported > > CLIENT: mount -o vers=4 server:/foo/bar /mnt > > SERVER: rm -r /foo > > CLIENT: > /mnt/baz # gets an error of course > > CLIENT: ls -l /mnt # error again > > CLIENT: umount /mnt > > > > The result of that last command is: > > > > /mnt was not found in /proc/mounts > > /mnt was not found in /proc/mounts > > > > Strange? > > > > cat /proc/mounts > > > > ..... > > 10.0.2.2://foo/bar /mnt\040(deleted) nfs4 rw,relatime,vers=4,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.0.2.15,minorversion=0,local_lock=none,addr=10.0.2.2 0 0 > > .... > > > > Notice the "\040(deleted)". > > > > NFS has unhashed that directory because it is obviously bad, and d_path() > > notices and adds " (deleted)". > > > > Now I might be able to argue that NFS shouldn't be unhashing a directory that > > is a mountpoint - it certainly seems strange behaviour. > > > > But I think I can more strongly argue that /proc/mounts shouldn't be showing > > the mounted directory, but instead the directory that it is mounted on. > > Obviously these both have the same name so it shouldn't matter ... except > > that here is a case where it does. > > > > I "fixed" it with > > > > --- a/fs/proc_namespace.c > > +++ b/fs/proc_namespace.c > > @@ -93,7 +93,7 @@ static int show_vfsmnt(struct seq_file *m, struct vfsmount *mnt) > > { > > struct mount *r = real_mount(mnt); > > int err = 0; > > - struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt }; > > + struct path mnt_path = { .dentry = r->mnt_mountpoint, .mnt = &(r->mnt_parent)->mnt }; > > struct super_block *sb = mnt_path.dentry->d_sb; > > > > if (sb->s_op->show_devname) { > > > > though I suspect that isn't safe and needs some locking. > > > > Probably both should be fixed: NFS should not invalidate any mounted > > directory, and show_vfsmnt() should report the mointpoint, not the mounted > > directory. > > > > I can't figure out any way to get NFS to not invalidate the mounted directory. > > I think it happens in nfs_lookup_revalidate() when it calls d_drop(), but I > > don't know how to tell if a given dentry is a mnt_root for any mountpoint. > > > > Suggestions? Thoughts? > > > > Thanks, > > NeilBrown > > > > I've also been looking at some weird ESTALE problems. Here's another > fun one that doesn't involve mountpoints. Assume here that we're > working in the same exported directory on client and server: > > server# mkdir a > client# cd a > server# mv a a.bak > client# sleep 30 # (or whatever the dir attrcache timeout is) > client# stat . > stat: cannot stat ‘.’: Stale NFS file handle > > Obviously, "." should not be stale. It got renamed, but the inode still > exists on the server. > > If you sniff on the wire, you'll see that the server doesn't ever send > an ESTALE here. What happens is that due to FS_REVAL_DOT being set, we > end up trying to revalidate the dentry that "." refers to. We find that > the parent changed (obviously) and then try to redo the lookup of "a". > At that point we notice that it doesn't exist and turn it into ESTALE. > > I don't really understand the point of FS_REVAL_DOT. What does that > actually buy us? I wonder if removing it would also help your testcase? > I think that is a slightly different issue, but certainly related. I have hit your problem before and have the following patch in SLES. I think I tried pushing it upstream, but didn't get much in the way of a useful response. (patch is space-damaged - don't try to apply with 'patch'). BTW I have another problem, related to this one and which could be fixed by removing FS_REVAL_DOT. If you mount -o vers=4,noac server:/some/path /mnt then stop nfsd on the server and umount /mnt it hangs. Partly it hangs because 'mount' tries to do a 'readlink' on the mountpoint. I can probably get it to not do that (or use --no-canonicalize). But then sys_umount hangs because it tries to check with the server that the thing being unmounted really is still a directory... I would be really nice if sys_unmount used a LOOKUP_MOUNTPOINT flag that works a bit like LOOKUP_PARENT and LOOKUP_NOFOLLOW in that it skips the very last step and returns the mounted-on directory, not the mountpoint that is mounted there - or at least makes sure not revalidate happens on that final mounted directory. I think FS_REVAL_DOT is needed so that if you call stat("."), it will update attributes from the server if the cache is old. However it seems to do a whole lot more than that, including "lookup" calls which it I'm sure is wrong. NeilBrown Subject: [PATCH] nfs - handle d_revalidate of 'dot' correctly. When d_revalidate is called on a dentry because FS_REVAL_DOT is set it isn't really appropriate to revalidate the name. If the path was simply ".", then the current-working-directory could have been renamed on the server and should still be accessible as "." even if it has a new name. If the path was "/some/long/path/.", then the final component ("path" in this case) has already been revalidated and there is no particular need to do it again. If we change nd->last_type to refer to "the last component looked at" rather than just "the last component", then these cases can be detected by "nd->last_type != LAST_NORM". Signed-off-by: NeilBrown --- fs/namei.c | 2 +- fs/nfs/dir.c | 9 +++++++++ 2 files changed, 10 insertions(+), 1 deletion(-) --- linux-3.0-SLE11-SP2.orig/fs/namei.c +++ linux-3.0-SLE11-SP2/fs/namei.c @@ -1460,6 +1460,7 @@ static int link_path_walk(const char *na } } + nd->last_type = type; /* remove trailing slashes? */ if (!c) goto last_component; @@ -1486,7 +1487,6 @@ last_component: /* Clear LOOKUP_CONTINUE iff it was previously unset */ nd->flags &= lookup_flags | ~LOOKUP_CONTINUE; nd->last = this; - nd->last_type = type; return 0; } terminate_walk(nd); --- linux-3.0-SLE11-SP2.orig/fs/nfs/dir.c +++ linux-3.0-SLE11-SP2/fs/nfs/dir.c @@ -1138,6 +1138,15 @@ static int nfs_lookup_revalidate(struct if (NFS_STALE(inode)) goto out_bad; + if (nd->last_type != LAST_NORM) { + /* name not relevant, just inode */ + error = nfs_revalidate_inode(NFS_SERVER(inode), inode); + if (error) + goto out_bad; + else + goto out_valid; + } + error = -ENOMEM; fhandle = nfs_alloc_fhandle(); fattr = nfs_alloc_fattr();