Subject: RE: [PATCH] [Bug 16494] NFS client over TCP hangs due to packet loss

From: "Andy Chittenden" <[email-masked]>
Date: Thu, 5 Aug 2010 15:55:17 +0100

> On 2010-08-03 10:11, Andrew Morton wrote:
> > (cc linux-nfs)
> >
> > On Tue, 03 Aug 2010 01:21:44 -0700 (PDT) David
> Miller<davem-fT/PcQaiUtIeIZ0/[email-masked]>  wrote:
> >
> >> From: "Andy Chittenden"<[email-masked]>
> >> Date: Tue, 3 Aug 2010 09:14:31 +0100
> >>
> >>> I don't know whether this patch is the correct fix or not but it
> enables the
> >>> NFS client to recover.
> >>>
> >>> Kernel version: 2.6.34.1 and 2.6.32.
> >>>
> >>> Fixes<https://bugzilla.kernel.org/show_bug.cgi?id=16494>. It clears
> down
> >>> any previous shutdown attempts so that reconnects on a socket
> that's been
> >>> shutdown leave the socket in a usable state (otherwise
> tcp_sendmsg() returns
> >>> -EPIPE).
> >>
> >> If the SunRPC code wants to close a TCP socket then use it again,
> >> it should disconnect by doing a connect() with sa_family ==
> AF_UNSPEC
> 
> There is code to do that in the SunRPC code in xs_abort_connection()
> but
> that's conditionally called from xs_tcp_reuse_connection():
> 
> static void xs_tcp_reuse_connection(struct rpc_xprt *xprt, struct
> sock_xprt *transport)
> {
> 	unsigned int state = transport->inet->sk_state;
> 
> 	if (state == TCP_CLOSE && transport->sock->state ==
> SS_UNCONNECTED)
> 		return;
> 	if ((1 << state) & (TCPF_ESTABLISHED|TCPF_SYN_SENT))
> 		return;
> 	xs_abort_connection(xprt, transport);
> }
> 
> That's changed since 2.6.26 where it unconditionally did the connect()
> with sa_family == AF_UNSPEC. FWIW we cannot reproduce this problem with
> 2.6.26.

The problem is fixed with this patch which also prints out that sk_shutdown
can be non-zero on entry to xs_tcp_reuse_connection:

# diff -up /home/company/software/src/linux-2.6.34.2/net/sunrpc/xprtsock.c
net/sunrpc/xprtsock.c 
--- /home/company/software/src/linux-2.6.34.2/net/sunrpc/xprtsock.c
2010-08-02 18:30:51.000000000 +0100
+++ net/sunrpc/xprtsock.c       2010-08-05 12:21:11.000000000 +0100
@@ -1322,10 +1322,11 @@ static void xs_tcp_state_change(struct s
        if (!(xprt = xprt_from_sock(sk)))
                goto out;
        dprintk("RPC:       xs_tcp_state_change client %p...\n", xprt);
-       dprintk("RPC:       state %x conn %d dead %d zapped %d\n",
+       dprintk("RPC:       state %x conn %d dead %d zapped %d sk_shutdown
%d\n",
                        sk->sk_state, xprt_connected(xprt),
                        sock_flag(sk, SOCK_DEAD),
-                       sock_flag(sk, SOCK_ZAPPED));
+                       sock_flag(sk, SOCK_ZAPPED),
+                       sk->sk_shutdown);
 
        switch (sk->sk_state) {
        case TCP_ESTABLISHED:
@@ -1796,10 +1797,18 @@ static void xs_tcp_reuse_connection(stru
 {
        unsigned int state = transport->inet->sk_state;
 
-       if (state == TCP_CLOSE && transport->sock->state == SS_UNCONNECTED)
-               return;
-       if ((1 << state) & (TCPF_ESTABLISHED|TCPF_SYN_SENT))
-               return;
+       if (state == TCP_CLOSE && transport->sock->state == SS_UNCONNECTED)
{
+               if (transport->inet->sk_shutdown == 0)
+                       return;
+               printk("%s: TCP_CLOSEd and sk_shutdown set to %d\n",
+                       __func__, transport->inet->sk_shutdown);
+       }
+       if ((1 << state) & (TCPF_ESTABLISHED|TCPF_SYN_SENT)) {
+               if (transport->inet->sk_shutdown == 0)
+                       return;
+               printk("%s: sk_shutdown set to %d\n",
+                       __func__, transport->inet->sk_shutdown);
+       }
        xs_abort_connection(xprt, transport);
 }

Signed-off-by: Andy Chittenden <[email-masked]>

dmesg displays:

[ 2840.896043] xs_tcp_reuse_connection: TCP_CLOSEd and sk_shutdown set to 2

so previously the code was attempting to reuse the connection but wasn't
aborting it and thus didn't clear down sk_shutdown.

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