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SubjectRE: [PATCH] [Bug 16494] NFS client over TCP hangs due to packet loss
Date
> 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@davemloft.net> wrote:
> >
> >> From: "Andy Chittenden"<andyc.bluearc@gmail.com>
> >> 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 <andyc.bluearc@gmail.com>
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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