linux-kernel - Re: [NFS] NFSv2/3 broken exporting/mounting (permission denied) in 2.6.24-rc4

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Date:	Fri, 7 Dec 2007 15:32:42 -0500
From:	Erez Zadok <ezk@...sunysb.edu>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	linux-kernel@...r.kernel.org, nfs@...ts.sourceforge.net,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [NFS] NFSv2/3 broken exporting/mounting (permission denied) in 2.6.24-rc4 

In message <20071207200655.GD2204@...ldses.org>, "J. Bruce Fields" writes:
> On Fri, Dec 07, 2007 at 03:00:13PM -0500, Erez Zadok wrote:
[...]
> Those files are actually in a separate filesystem (of type "nfsd") which
> is supposed to be mounted on /proc/fs/nfsd/.   So that mount must have
> failed in the bad case?  It's not immediately obvious to me what this
> patch has to do with that.  Hm.

Yes, it is indeed a separate mount in both cases, but in the broken case,
/proc/fs/nfsd is empty.

The patch in question introduces a proc ->d_revalidate method which does
this:

static int proc_revalidate_dentry(struct dentry *dentry, struct nameidata *nd)
{
	d_drop(dentry);
	return 0;
}

I'm not sure why it drops the dentry and then returns OK to the VFS; is it
to force the VFS to revalidate the dentry?  In that case, I think it should
return -ESTALE.  I also don't know why /proc needs a ->d_revalidate in the
first place (it was fine up until now).  Perhaps what proc does now is
correct, but its behavior has changed such that nfsd's /proc/fs/nfsd needs
to do something different (like grab an extra dentry ref?).

Anyway, if I comment out the d_drop line in proc_revalidate_dentry, or
remove proc's ->d_revalidate method, nfs exporting works again.

Someone more familiar with this patch and /proc should investigate.  Until
then, nfsv2/3 exporting are broken in 2.6.24-rc4.

> --b.

Cheers,
Erez.
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