linux-kernel - Re: [PATCH 4/5] SUNRPC: track when a client connection is routed to the local host.

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Message-ID: <20140424091419.0ba0cfd3@notabene.brown>
Date:	Thu, 24 Apr 2014 09:14:19 +1000
From:	NeilBrown <neilb@...e.de>
To:	Anna Schumaker <Anna.Schumaker@...app.com>
Cc:	Jan Kara <jack@...e.cz>, Jeff Layton <jlayton@...hat.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"Dave Chinner" <david@...morbit.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"Mel Gorman" <mgorman@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-mm@...ck.org>, <linux-nfs@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] SUNRPC: track when a client connection is routed to
 the local host.

On Wed, 23 Apr 2014 09:44:12 -0400 Anna Schumaker <Anna.Schumaker@...app.com>
wrote:

> On 04/22/2014 10:40 PM, NeilBrown wrote:
> > If requests are being sent to the local host, then NFS will
> > need to take care to avoid deadlocks.
> >
> > So keep track when accepting a connection or sending a UDP request
> > and set a flag in the svc_xprt when the peer connected to is local.
> >
> > The interface rpc_is_foreign() is provided to check is a given client
> > is connected to a foreign server.  When it returns zero it is either
> > not connected or connected to a local server and in either case
> > greater care is needed.
> >
> > Signed-off-by: NeilBrown <neilb@...e.de>
> > ---
> >  include/linux/sunrpc/clnt.h |    1 +
> >  include/linux/sunrpc/xprt.h |    1 +
> >  net/sunrpc/clnt.c           |   25 +++++++++++++++++++++++++
> >  net/sunrpc/xprtsock.c       |   17 +++++++++++++++++
> >  4 files changed, 44 insertions(+)
> >
> > diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
> > index 8af2804bab16..5d626cc5ab01 100644
> > --- a/include/linux/sunrpc/clnt.h
> > +++ b/include/linux/sunrpc/clnt.h
> > @@ -173,6 +173,7 @@ void		rpc_force_rebind(struct rpc_clnt *);
> >  size_t		rpc_peeraddr(struct rpc_clnt *, struct sockaddr *, size_t);
> >  const char	*rpc_peeraddr2str(struct rpc_clnt *, enum rpc_display_format_t);
> >  int		rpc_localaddr(struct rpc_clnt *, struct sockaddr *, size_t);
> > +int		rpc_is_foreign(struct rpc_clnt *);
> >  
> >  #endif /* __KERNEL__ */
> >  #endif /* _LINUX_SUNRPC_CLNT_H */
> > diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
> > index 8097b9df6773..318ee37bc358 100644
> > --- a/include/linux/sunrpc/xprt.h
> > +++ b/include/linux/sunrpc/xprt.h
> > @@ -340,6 +340,7 @@ int			xs_swapper(struct rpc_xprt *xprt, int enable);
> >  #define XPRT_CONNECTION_ABORT	(7)
> >  #define XPRT_CONNECTION_CLOSE	(8)
> >  #define XPRT_CONGESTED		(9)
> > +#define XPRT_LOCAL		(10)
> >  
> >  static inline void xprt_set_connected(struct rpc_xprt *xprt)
> >  {
> > diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> > index 0edada973434..454cea69b373 100644
> > --- a/net/sunrpc/clnt.c
> > +++ b/net/sunrpc/clnt.c
> > @@ -1109,6 +1109,31 @@ const char *rpc_peeraddr2str(struct rpc_clnt *clnt,
> >  }
> >  EXPORT_SYMBOL_GPL(rpc_peeraddr2str);
> >  
> > +/**
> > + * rpc_is_foreign - report is rpc client was recently connected to
> > + *                  remote host
> > + * @clnt: RPC client structure
> > + *
> > + * If the client is not connected, or connected to the local host
> > + * (any IP address), then return 0.  Only return non-zero if the
> > + * most recent state was a connection to a remote host.
> > + * For UDP the client always appears to be connected, and the
> > + * remoteness of the host is of the destination of the last transmission.
> > + */
> > +int rpc_is_foreign(struct rpc_clnt *clnt)
> > +{
> > +	struct rpc_xprt *xprt;
> > +	int conn_foreign;
> > +
> > +	rcu_read_lock();
> > +	xprt = rcu_dereference(clnt->cl_xprt);
> > +	conn_foreign = (xprt && xprt_connected(xprt)
> > +			&& !test_bit(XPRT_LOCAL, &xprt->state));
> > +	rcu_read_unlock();
> > +	return conn_foreign;
> > +}
> > +EXPORT_SYMBOL_GPL(rpc_is_foreign);
> > +
> >  static const struct sockaddr_in rpc_inaddr_loopback = {
> >  	.sin_family		= AF_INET,
> >  	.sin_addr.s_addr	= htonl(INADDR_ANY),
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index 0addefca8e77..74796cf37d5b 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -642,6 +642,15 @@ static int xs_udp_send_request(struct rpc_task *task)
> >  			xdr->len - req->rq_bytes_sent, status);
> >  
> >  	if (status >= 0) {
> > +		struct dst_entry *dst;
> > +		rcu_read_lock();
> > +		dst = rcu_dereference(transport->sock->sk->sk_dst_cache);
> > +		if (dst && dst->dev && (dst->dev->features & NETIF_F_LOOPBACK))
> > +			set_bit(XPRT_LOCAL, &xprt->state);
> > +		else
> > +			clear_bit(XPRT_LOCAL, &xprt->state);
> > +		rcu_read_unlock();
> > +
> You repeat this block of code a bit later.  Can you please make it an inline helper function?

Thanks for the suggestion.
I've put

static inline int sock_is_loopback(struct sock *sk)
{
	struct dst_entry *dst;
	int loopback = 0;
	rcu_read_lock();
	dst = rcu_dereference(sk->sk_dst_cache);
	if (dst && dst->dev &&
	    (dst->dev->features & NETIF_F_LOOPBACK))
		loopback = 1;
	rcu_read_unlock();
	return loopback;
}


in sunrpc.h, and used it for both the server-side and the client side.

NeilBrown

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