Re: [PATCH 10/10] nfsd: clients don't need to break their own delegations

From: bfields@fieldses.org (J. Bruce Fields)
To: David Howells <dhowells@redhat.com>
Cc: "J. Bruce Fields" <bfields@redhat.com>,
	linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 10/10] nfsd: clients don't need to break their own delegations
Date: Tue, 20 Mar 2018 10:52:54 -0400	[thread overview]
Message-ID: <20180320145254.GB4288@fieldses.org> (raw)
In-Reply-To: <29167.1521552951@warthog.procyon.org.uk>

On Tue, Mar 20, 2018 at 01:35:51PM +0000, David Howells wrote:
> J. Bruce Fields <bfields@redhat.com> wrote:
> 
> > @@ -139,6 +139,9 @@ struct cred {
> >  	struct key	*thread_keyring; /* keyring private to this thread */
> >  	struct key	*request_key_auth; /* assumed request_key authority */
> >  #endif
> > +#ifdef CONFIG_FILE_LOCKING
> > +	void		*lease_breaker; /* identify NFS client breaking a delegation */
> > +#endif
> >  #ifdef CONFIG_SECURITY
> >  	void		*security;	/* subjective LSM security */
> >  #endif
> 
> Sorry, but ewww.

I'm sure you're right, but, to make sure I understand:

> Two reasons for that comment:
> 
>  (1) The cred struct may get retained long past where you expect if it gets
>      attached to another process or a file descriptor.

How would that happen in the case of a knfsd thread?

>  (2) The ->lease_breaker pointer needs lifetime management in cred.c.  It will
>      potentially get copied around and may need cleaning up.

Hm, OK.

> Can you stick your breaker identity in a key struct as Jeff suggested?

Probably so.  I'm unfamiliar with the keyring code.  How would you
recommend doing that?

--b.