[PATCH 0/2] SUNRPC: Clean up port reuse behavior on reconnects

[PATCH 0/2] SUNRPC: Clean up port reuse behavior on reconnects

[Vallish Vaidyeshwara]

We have seen examples of NFSv4 client reconnections failing due to
client source port reuse combined with stateful TCP state tracking in
middleboxes.

Commit 0f7a622ca616 ("rpc: xs_bind - do not bind when requesting a
random ephemeral port"), commit 4dda9c8a5e34 ("SUNRPC: Set SO_REUSEPORT
socket option for TCP connections"), and commit 1f4c17a03ba7 ("SUNRPC:
Handle EADDRNOTAVAIL on connection failures") had unintended side effects
of making port reuse dependent on whether that client uses reserved or
non-reserved source ports.

This series fixes the observed NFSv4 client reconnect failures by
choosing a new source port regardless of which port range is in use
for RST or FIN terminating the prior connection. This series does
not restore the original always-reuse behavior that existed prior to
commits mentioned above.

Patch 1:
--------
SUNRPC: Need to reuse non-reserved port for reconnect

This patch restores the original behavior of port reuse in all
scenarios.

Patch 2:
--------
SUNRPC: Reconnect with new port on server initiated connection
    termination

Client uses a new port only in cases where server has terminated
the connection explicitly using RST or FIN.

Proposed outcome with this patch series:
----------------------------------------
------------------------------------------------------------------
| Port type | Connection termination | Current    | With this    |
|           |         type           | behavior   | patch series |
------------------------------------------------------------------
|  Reserved | Network partition-DROP | Reuse port | Reuse port   |
------------------------------------------------------------------
|  Reserved | FIN from server        | Reuse port | New port     |
------------------------------------------------------------------
|  Reserved | RST from server        | Reuse port | New port     |
------------------------------------------------------------------
|  Non-Resv | Network partition-DROP | New port   | Reuse port   |
------------------------------------------------------------------
|  Non-Resv | FIN from server        | New port   | New port     |
------------------------------------------------------------------
|  Non-Resv | RST from server        | New port   | New port     |
------------------------------------------------------------------

 net/sunrpc/xprtsock.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

-- 
2.7.3.AMZN

[PATCH 1/2] SUNRPC: Need to reuse non-reserved port for reconnect

[Vallish Vaidyeshwara]

Seemingly innocent optimization related to xs_bind() broke TCP port
reuse by making non-reserved ephermal socket port to not be saved
in "struct sock_xprt (srcport)". In case of non-reserved port,
allocation happens as part of kernel_connect() inside of
xs_tcp_finish_connecting(). kernel_connect() returns EINPROGRESS
and the code skips stashing srcport in sock_xprt for reconnects.
This affects servers DRC in case of network partition where client's
RPC recovery would try reconnecting with a different port.

Reported-by: Alexey Kuznetsov <alexeyk@amazon.com>
Reviewed-by: Jacob Strauss <jsstraus@amazon.com>
Reviewed-by: Alakesh Haloi <alakeshh@amazon.com>
Signed-off-by: Vallish Vaidyeshwara <vallish@amazon.com>
Fixes: 0f7a622c ("rpc: xs_bind - do not bind when requesting a random ephemeral port")
---
 net/sunrpc/xprtsock.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index c8902f1..5bf75b3 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -2393,9 +2393,11 @@ static int xs_tcp_finish_connecting(struct rpc_xprt *xprt, struct socket *sock)
 	ret = kernel_connect(sock, xs_addr(xprt), xprt->addrlen, O_NONBLOCK);
 	switch (ret) {
 	case 0:
-		xs_set_srcport(transport, sock);
 		/* fall through */
 	case -EINPROGRESS:
+		/* Allocated port saved for reconnect */
+		xs_set_srcport(transport, sock);
+
 		/* SYN_SENT! */
 		if (xprt->reestablish_timeout < XS_TCP_INIT_REEST_TO)
 			xprt->reestablish_timeout = XS_TCP_INIT_REEST_TO;
-- 
2.7.3.AMZN

Re: [PATCH 1/2] SUNRPC: Need to reuse non-reserved port for reconnect

[Vallish Vaidyeshwara]

On Thu, May 10, 2018 at 06:12:53AM +0000, Vallish Vaidyeshwara wrote:
> Seemingly innocent optimization related to xs_bind() broke TCP port
> reuse by making non-reserved ephermal socket port to not be saved
> in "struct sock_xprt (srcport)". In case of non-reserved port,
> allocation happens as part of kernel_connect() inside of
> xs_tcp_finish_connecting(). kernel_connect() returns EINPROGRESS
> and the code skips stashing srcport in sock_xprt for reconnects.
> This affects servers DRC in case of network partition where client's
> RPC recovery would try reconnecting with a different port.
> 
> Reported-by: Alexey Kuznetsov <alexeyk@amazon.com>
> Reviewed-by: Jacob Strauss <jsstraus@amazon.com>
> Reviewed-by: Alakesh Haloi <alakeshh@amazon.com>
> Signed-off-by: Vallish Vaidyeshwara <vallish@amazon.com>
> Fixes: 0f7a622c ("rpc: xs_bind - do not bind when requesting a random ephemeral port")
> ---
>  net/sunrpc/xprtsock.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index c8902f1..5bf75b3 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2393,9 +2393,11 @@ static int xs_tcp_finish_connecting(struct rpc_xprt *xprt, struct socket *sock)
>  	ret = kernel_connect(sock, xs_addr(xprt), xprt->addrlen, O_NONBLOCK);
>  	switch (ret) {
>  	case 0:
> -		xs_set_srcport(transport, sock);
>  		/* fall through */
>  	case -EINPROGRESS:
> +		/* Allocated port saved for reconnect */
> +		xs_set_srcport(transport, sock);
> +
>  		/* SYN_SENT! */
>  		if (xprt->reestablish_timeout < XS_TCP_INIT_REEST_TO)
>  			xprt->reestablish_timeout = XS_TCP_INIT_REEST_TO;
> -- 
> 2.7.3.AMZN
>

Hello Trond and Bruce,

This patch is actually restoring existing broken DRC behavior. Can you folks
let me know your feedback on this patch as well.

Thanks.
-Vallish

[PATCH 2/2] SUNRPC: Reconnect with new port on server initiated connection termination

[Vallish Vaidyeshwara]

Server initiated socket close can corrupt connection state tracking
table in conjunction with other network middle boxes. In situations
like these, client connection hangs till connection state tracking
table entries age out and get purged. Client reconnection with a new
port in such a situation will avoid connection hang.

Reviewed-by: Jacob Strauss <jsstraus@amazon.com>
Reviewed-by: Alakesh Haloi <alakeshh@amazon.com>
Signed-off-by: Vallish Vaidyeshwara <vallish@amazon.com>
---
 net/sunrpc/xprtsock.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 5bf75b3..d293c8d 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -1629,6 +1629,8 @@ static void xs_tcp_state_change(struct sock *sk)
 		/* The server initiated a shutdown of the socket */
 		xprt->connect_cookie++;
 		clear_bit(XPRT_CONNECTED, &xprt->state);
+		/* Server sent FIN, reconnect with a new port */
+		transport->srcport = 0;
 		xs_tcp_force_close(xprt);
 		/* fall through */
 	case TCP_CLOSING:
@@ -1650,6 +1652,9 @@ static void xs_tcp_state_change(struct sock *sk)
 					&transport->sock_state))
 			xprt_clear_connecting(xprt);
 		clear_bit(XPRT_CLOSING, &xprt->state);
+		/* Server sent RST, reconnect with a new port */
+		if (sk->sk_err == ECONNRESET)
+			transport->srcport = 0;
 		if (sk->sk_err)
 			xprt_wake_pending_tasks(xprt, -sk->sk_err);
 		/* Trigger the socket release */
-- 
2.7.3.AMZN

Re: [PATCH 2/2] SUNRPC: Reconnect with new port on server initiated connection termination

[Trond Myklebust]

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Re: [PATCH 2/2] SUNRPC: Reconnect with new port on server initiated connection termination

[Vallish Vaidyeshwara]

On Thu, May 10, 2018 at 03:25:14PM +0000, Trond Myklebust wrote:
> On Thu, 2018-05-10 at 06:12 +0000, Vallish Vaidyeshwara wrote:
> > Server initiated socket close can corrupt connection state tracking
> > table in conjunction with other network middle boxes. In situations
> > like these, client connection hangs till connection state tracking
> > table entries age out and get purged. Client reconnection with a new
> > port in such a situation will avoid connection hang.
> > 
> > Reviewed-by: Jacob Strauss <jsstraus@amazon.com>
> > Reviewed-by: Alakesh Haloi <alakeshh@amazon.com>
> > Signed-off-by: Vallish Vaidyeshwara <vallish@amazon.com>
> > ---
> >  net/sunrpc/xprtsock.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index 5bf75b3..d293c8d 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -1629,6 +1629,8 @@ static void xs_tcp_state_change(struct sock
> > *sk)
> >  		/* The server initiated a shutdown of the socket */
> >  		xprt->connect_cookie++;
> >  		clear_bit(XPRT_CONNECTED, &xprt->state);
> > +		/* Server sent FIN, reconnect with a new port */
> > +		transport->srcport = 0;
> >  		xs_tcp_force_close(xprt);
> >  		/* fall through */
> >  	case TCP_CLOSING:
> > @@ -1650,6 +1652,9 @@ static void xs_tcp_state_change(struct sock
> > *sk)
> >  					&transport->sock_state))
> >  			xprt_clear_connecting(xprt);
> >  		clear_bit(XPRT_CLOSING, &xprt->state);
> > +		/* Server sent RST, reconnect with a new port */
> > +		if (sk->sk_err == ECONNRESET)
> > +			transport->srcport = 0;
> >  		if (sk->sk_err)
> >  			xprt_wake_pending_tasks(xprt, -sk->sk_err);
> >  		/* Trigger the socket release */
> 
> NACK. This will utterly break NFSv2, NFSv3 and NFSv4.0 duplicate replay
> cache semantics. 
> 
> Cheers
>   Trond
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com

Hello Trond,

The first patch in this series is actually helping restore DRC behavior in
cases like network partition where packets are dropped:
[PATCH 1/2] SUNRPC: Need to reuse non-reserved port for reconnect
Patch 1 starts reusing port in all cases.

The second patch is still not breaking DRC semantics, to quote from source
code:

<code snip>
  /**
   * xs_close - close a socket
   * @xprt: transport
   *
   * This is used when all requests are complete; ie, no DRC state remains
   * on the server we want to save.
   *
   * The caller _must_ be holding XPRT_LOCKED in order to avoid issues with
   * xs_reset_transport() zeroing the socket from underneath a writer.
   */
  static void xs_close(struct rpc_xprt *xprt)
<code snip>

If the server has closed a connection, then no DRC state remains on the server
we want to use.

The second patch is exploiting this semantics and using a new port in following
2 cases:
a) RST from server implies the connection was torn down & no useful DRC exists
on server
b) FIN from server implies that server is shutting down the connection as part
of close and no DRC state remains

Please let me know if I have missed something obvious, I definitely do not want
to break DRC as that is not the intention of this patch series. Is there a
situation where server can close a connection and still keep DRC?

Thanks.
-Vallish

Re: [PATCH 2/2] SUNRPC: Reconnect with new port on server initiated connection termination

[Trond Myklebust]

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Re: [PATCH 2/2] SUNRPC: Reconnect with new port on server initiated connection termination

[Vallish Vaidyeshwara]

On Thu, May 10, 2018 at 05:26:12PM +0000, Trond Myklebust wrote:
> On Thu, 2018-05-10 at 16:22 +0000, Vallish Vaidyeshwara wrote:
> > On Thu, May 10, 2018 at 03:25:14PM +0000, Trond Myklebust wrote:
> > > On Thu, 2018-05-10 at 06:12 +0000, Vallish Vaidyeshwara wrote:
> > > > Server initiated socket close can corrupt connection state
> > > > tracking
> > > > table in conjunction with other network middle boxes. In
> > > > situations
> > > > like these, client connection hangs till connection state
> > > > tracking
> > > > table entries age out and get purged. Client reconnection with a
> > > > new
> > > > port in such a situation will avoid connection hang.
> > > > 
> > > > Reviewed-by: Jacob Strauss <jsstraus@amazon.com>
> > > > Reviewed-by: Alakesh Haloi <alakeshh@amazon.com>
> > > > Signed-off-by: Vallish Vaidyeshwara <vallish@amazon.com>
> > > > ---
> > > >  net/sunrpc/xprtsock.c | 5 +++++
> > > >  1 file changed, 5 insertions(+)
> > > > 
> > > > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > > > index 5bf75b3..d293c8d 100644
> > > > --- a/net/sunrpc/xprtsock.c
> > > > +++ b/net/sunrpc/xprtsock.c
> > > > @@ -1629,6 +1629,8 @@ static void xs_tcp_state_change(struct sock
> > > > *sk)
> > > >  		/* The server initiated a shutdown of the socket
> > > > */
> > > >  		xprt->connect_cookie++;
> > > >  		clear_bit(XPRT_CONNECTED, &xprt->state);
> > > > +		/* Server sent FIN, reconnect with a new port */
> > > > +		transport->srcport = 0;
> > > >  		xs_tcp_force_close(xprt);
> > > >  		/* fall through */
> > > >  	case TCP_CLOSING:
> > > > @@ -1650,6 +1652,9 @@ static void xs_tcp_state_change(struct sock
> > > > *sk)
> > > >  					&transport->sock_state))
> > > >  			xprt_clear_connecting(xprt);
> > > >  		clear_bit(XPRT_CLOSING, &xprt->state);
> > > > +		/* Server sent RST, reconnect with a new port */
> > > > +		if (sk->sk_err == ECONNRESET)
> > > > +			transport->srcport = 0;
> > > >  		if (sk->sk_err)
> > > >  			xprt_wake_pending_tasks(xprt, -sk-
> > > > >sk_err);
> > > >  		/* Trigger the socket release */
> > > 
> > > NACK. This will utterly break NFSv2, NFSv3 and NFSv4.0 duplicate
> > > replay
> > > cache semantics. 
> > > 
> > > Cheers
> > >   Trond
> > > -- 
> > > Trond Myklebust
> > > Linux NFS client maintainer, Hammerspace
> > > trond.myklebust@hammerspace.com
> > 
> > Hello Trond,
> > 
> > The first patch in this series is actually helping restore DRC
> > behavior in
> > cases like network partition where packets are dropped:
> > [PATCH 1/2] SUNRPC: Need to reuse non-reserved port for reconnect
> > Patch 1 starts reusing port in all cases.
> > 
> > The second patch is still not breaking DRC semantics, to quote from
> > source
> > code:
> > 
> > <code snip>
> >   /**
> >    * xs_close - close a socket
> >    * @xprt: transport
> >    *
> >    * This is used when all requests are complete; ie, no DRC state
> > remains
> >    * on the server we want to save.
> >    *
> >    * The caller _must_ be holding XPRT_LOCKED in order to avoid
> > issues with
> >    * xs_reset_transport() zeroing the socket from underneath a
> > writer.
> >    */
> >   static void xs_close(struct rpc_xprt *xprt)
> > <code snip>
> > 
> > If the server has closed a connection, then no DRC state remains on
> > the server
> > we want to use.
> > 
> > The second patch is exploiting this semantics and using a new port in
> > following
> > 2 cases:
> > a) RST from server implies the connection was torn down & no useful
> > DRC exists
> > on server
> > b) FIN from server implies that server is shutting down the
> > connection as part
> > of close and no DRC state remains
> > 
> > Please let me know if I have missed something obvious, I definitely
> > do not want
> > to break DRC as that is not the intention of this patch series. Is
> > there a
> > situation where server can close a connection and still keep DRC?
> > 
> 
> The DRC does not exist for the benefit of the server, but for the
> benefit of the client. It is there to ensure that if the client replays
> the request, then it gets the exact same reply as it should have
> received when the first request was sent. Bearing that in mind:
> 
>    1. What guarantees that all servers behave correctly w.r.t. ensuring
>       that they have sent all replies to any outstanding RPC call before
>       shutting down the connection. I'm not sure that even the Linux
>       server does that.
>    2. How would a server even know whether or not the client may need to
>       replay a request?
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com

Hello Trond,

Thanks for the explanation, I was kind of misled by code comments in
xs_close.I will probably submit a different patch to clean up these code
comments which can mislead others as well.

Regards,
-Vallish

Re: [PATCH 2/2] SUNRPC: Reconnect with new port on server initiated connection termination

[bfields]

On Thu, May 10, 2018 at 04:22:02PM +0000, Vallish Vaidyeshwara wrote:
> If the server has closed a connection, then no DRC state remains on the server
> we want to use.

That's not a rule, as far as I know.  Certainly the Linux server doesn't
destroy DRC state on closing a connection.  (Should it? I'm not sure
that's a good idea.)

--b.

Re: [PATCH 2/2] SUNRPC: Reconnect with new port on server initiated connection termination

[Vallish Vaidyeshwara]

On Thu, May 10, 2018 at 01:37:28PM -0400, bfields@fieldses.org wrote:
> On Thu, May 10, 2018 at 04:22:02PM +0000, Vallish Vaidyeshwara wrote:
> > If the server has closed a connection, then no DRC state remains on the server
> > we want to use.
> 
> That's not a rule, as far as I know.  Certainly the Linux server doesn't
> destroy DRC state on closing a connection.  (Should it? I'm not sure
> that's a good idea.)
> 
> --b.
> 

Thanks for the clarification and I agree patch 2 should not be applied.