linux-kernel - Re: [RFC/PATCH 2/8] revoke: inode revoke lock V7

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Date:	Tue, 18 Dec 2007 09:31:03 +0200 (EET)
From:	Pekka J Enberg <penberg@...helsinki.fi>
To:	serge@...lyn.com
cc:	alan@...hat.com, viro@...iv.linux.org.uk, hch@...radead.org,
	peterz@...radead.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC/PATCH 2/8] revoke: inode revoke lock V7

Hi Serge,

(Thanks for looking at this. I appreciate the review!)

On Mon, 17 Dec 2007, serge@...lyn.com wrote:
> >  	struct vfsmount *mnt = nd->mnt;
> > -	struct dentry *dentry = __d_lookup(nd->dentry, name);
> > +	struct dentry *dentry;
> >  
> > +again:
> > +	dentry  = __d_lookup(nd->dentry, name);
> >  	if (!dentry)
> >  		goto need_lookup;
> > +
> > +	if (dentry->d_inode && IS_REVOKE_LOCKED(dentry->d_inode)) {
> 
> not sure whether this is a problem or not, but dentry->d_inode isn't
> locked here, right?  So nothing is keeping do_lookup() returning
> with an inode which gets revoked between here and the return 0
> a few lines down?

I assume you mean S_REVOKE_LOCK and not ->i_mutex, right?

The caller is supposed to block open(2) with chmod(2)/chattr(2) so while 
revoke is in progress, you can get references to the _revoked inode_, 
which is fine (operations on it will fail with EBADFS). The 
->i_revoke_wait bits are there to make sure that while we revoke, you 
can't get a _new reference_ to the inode until we're done.

			Pekka
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