linux-kernel - Re: Regression with initramfs and nfsroot (appears to be in the dcache)

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Message-ID: <20121130013628.GZ4939@ZenIV.linux.org.uk>
Date:	Fri, 30 Nov 2012 01:36:28 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Patrick McLean <patrick@....mcgill.ca>
Cc:	Patrick McLean <patrickm@...kai.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-nfs@...r.kernel.org
Subject: Re: Regression with initramfs and nfsroot (appears to be in the
 dcache)

On Thu, Nov 29, 2012 at 04:57:19PM -0800, Patrick McLean wrote:
> > Interesting...  Server-side that should've been produced by
> > encode_entryplus_baggage(), which looks like failing compose_entry_fh()...
> > which has explicit
> >         if (d_mountpoint(dchild))
> >                 goto out;
> > resulting in ENOENT on everything that's overmounted on server.
> > 
> > Do you, by any chance, have the server really exporting its own root
> > filesystem?  Another thing to check: have nfs_prime_dcache() print
> > filename.name of everything that fails nfs_same_entry() and has
> > zero entry->fh->size, regardless of d_invalidate() results.
> 
> The server is running 3.6.6 and is just exporting a subdir of an xfs filesystem (which does not happen to be the root filesystem).
> 
> The client is running as a KVM guest on the machine that is serving the NFS. I am reproducing this by booting the guest via an initramfs, and doing
> "ls /" at in single user mode.
> 
> I added a check that prints the filename.name of everything that fails nfs_same_file, and it appears to just be triggered by the same filesystems that
> are triggering the WARN_ON, the relevant dmesg is below.

[the same /dev, /proc and /sys]

	Very interesting.  Do you have anything mounted on the corresponding
directories on server?  The picture looks like you are getting empty
fhandles in readdir+ respons for exactly the same directories that happen
to be mountpoints on client.  In any case, we shouldn't do that blind
d_drop() - empty fhandles can happen.  The only remaining question is
why do they happen on that set of entries.  From my reading of
encode_entryplus_baggage() it looks like we have compose_entry_fh()
failing for those entries and those entries alone.  One possible cause
would be d_mountpoint(dchild) being true on server.  If it is true, we
can declare the case closed; if not, I really wonder what's going on.

Note that if the same fs is mounted elsewhere, d_mountpoint() would mean
that something is mounted on top of that directory in _some_ instance;
not necessary the exported one.  Can you slap printks on fs/nfsd/nfs3xdr.c
compose_entry_fh() failure exits and see which one triggers server-side?
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