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

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

[Andy Chittenden]

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).

# diff -up /home/company/software/src/linux-2.6.34.1/net/ipv4/tcp_output.c
net/ipv4
--- /home/company/software/src/linux-2.6.34.1/net/ipv4/tcp_output.c
2010-07-27 08:46:46.917000000 +0100
+++ net/ipv4/tcp_output.c       2010-07-27 09:19:16.000000000 +0100
@@ -2522,6 +2522,13 @@ static void tcp_connect_init(struct sock
        struct tcp_sock *tp = tcp_sk(sk);
        __u8 rcv_wscale;

+       /* clear 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).
+        */
+       sk->sk_shutdown = 0;
+
        /* We'll fix this up when we get a response from the other end.
         * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
         */

Signed-off-by: Andy Chittenden <andyc.bluearc@gmail.com>

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

[David Miller]

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

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

[Andrew Morton]

(cc linux-nfs)

On Tue, 03 Aug 2010 01:21:44 -0700 (PDT) David Miller <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org> wrote:

> From: "Andy Chittenden" <andyc.bluearc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> 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
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Re: [PATCH] [Bug 16494] NFS client over TCP hangs due to packet loss

[Andy Chittenden]

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/mPfg9Q@public.gmane.org>  wrote:
>
>> From: "Andy Chittenden"<andyc.bluearc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> 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.


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

[Andy Chittenden]

> 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/mPfg9Q@public.gmane.org>  wrote:
> >
> >> From: "Andy Chittenden"<andyc.bluearc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> >> 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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

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

[Trond Myklebust]

On Thu, 2010-08-05 at 15:55 +0100, Andy Chittenden wrote:
> > 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/mPfg9Q@public.gmane.org>  wrote:
> > >
> > >> From: "Andy Chittenden"<andyc.bluearc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > >> 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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> 
> 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.

Hi Andy,

I note that you are adding in two new printk()s. Why should they be
printk(), and not dprintk()? Are you trying to report an exception that
the user needs to be aware of, or is this only debugging info that we'll
want to turn off under normal operation?

Also, it might be useful to add a comment to the code here to remind us
what the 'sk_shutdown == 0' case corresponds to as far as the socket
state is concerned, so that the casual reader can see why we shouldn't
reset the connection.

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

[Andy Chittenden]

> On Thu, 2010-08-05 at 15:55 +0100, Andy Chittenden wrote:
> > > 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/mPfg9Q@public.gmane.org>  wrote:
> > > >
> > > >> From: "Andy Chittenden"<andyc.bluearc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > > >> 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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> >
> > 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.
> 
> Hi Andy,
> 
> I note that you are adding in two new printk()s. Why should they be
> printk(), and not dprintk()? Are you trying to report an exception that
> the user needs to be aware of, or is this only debugging info that
> we'll
> want to turn off under normal operation?

Hi Trond

Thanks for replying. It was debugging info: the printk()s show what the problem is. I was half expecting someone to pipe up "that isn't the correct way to fix this" and suggest another avenue to look at, or even, hopefully, come up with an alternative appropriate patch as I'm not an expert in this code: I don't know whether the sk_shutdown field being left set has implications elsewhere in the sunrpc code. FWIW I left the test case running overnight and have had only 50 such messages logged so it's not a heavy printk() load.

> 
> Also, it might be useful to add a comment to the code here to remind us
> what the 'sk_shutdown == 0' case corresponds to as far as the socket
> state is concerned, so that the casual reader can see why we shouldn't
> reset the connection.

If I knew what sk_shutdown == 0 really corresponded to, I could well add a comment! :-). I just knew that in 2.6.26 we didn't see this problem and that in later kernels the connection abort sequence was being done conditionally and that the sk_shutdown flag being left set was making tcp_sendmsg return an error. So, putting two and two together, I've effectively just added another condition in which to abort the connection.

As nobody has objected to the essence of my patch, I'll attempt a new patch that changes those printk()s into dprintk() and drop in what I think are appropriate comments. So here's a revised patch:

# 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       2010-08-06 08:09:08.000000000 +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 +1797,25 @@ 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) {
+               /* we don't need to abort the connection if the socket
+                * hasn't undergone a shutdown
+                */
+               if (transport->inet->sk_shutdown == 0)
+                       return;
+               dprintk("RPC:       %s: TCP_CLOSEd and sk_shutdown set to %d\n",
+                       __func__, transport->inet->sk_shutdown);
+       }
+       if ((1 << state) & (TCPF_ESTABLISHED|TCPF_SYN_SENT)) {
+               /* we don't need to abort the connection if the socket
+                * hasn't undergone a shutdown
+                */
+               if (transport->inet->sk_shutdown == 0)
+                       return;
+               dprintk("RPC:       %s: ESTABLISHED/SYN_SENT "
+                               "sk_shutdown set to %d\n",
+                               __func__, transport->inet->sk_shutdown);
+       }
        xs_abort_connection(xprt, transport);
 }

Signed-off-by: Andy Chittenden <andyc.bluearc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>


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

[Andy Chittenden]

> > On Thu, 2010-08-05 at 15:55 +0100, Andy Chittenden wrote:
> > > > 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.
> >
> > Hi Andy,
> >
> > I note that you are adding in two new printk()s. Why should they be
> > printk(), and not dprintk()? Are you trying to report an exception
> that
> > the user needs to be aware of, or is this only debugging info that
> > we'll
> > want to turn off under normal operation?
> 
> Hi Trond
> 
> Thanks for replying. It was debugging info: the printk()s show what the
> problem is. I was half expecting someone to pipe up "that isn't the
> correct way to fix this" and suggest another avenue to look at, or
> even, hopefully, come up with an alternative appropriate patch as I'm
> not an expert in this code: I don't know whether the sk_shutdown field
> being left set has implications elsewhere in the sunrpc code. FWIW I
> left the test case running overnight and have had only 50 such messages
> logged so it's not a heavy printk() load.
> 
> >
> > Also, it might be useful to add a comment to the code here to remind
> us
> > what the 'sk_shutdown == 0' case corresponds to as far as the socket
> > state is concerned, so that the casual reader can see why we
> shouldn't
> > reset the connection.
> 
> If I knew what sk_shutdown == 0 really corresponded to, I could well
> add a comment! :-). I just knew that in 2.6.26 we didn't see this
> problem and that in later kernels the connection abort sequence was
> being done conditionally and that the sk_shutdown flag being left set
> was making tcp_sendmsg return an error. So, putting two and two
> together, I've effectively just added another condition in which to
> abort the connection.
> 
> As nobody has objected to the essence of my patch, I'll attempt a new
> patch that changes those printk()s into dprintk() and drop in what I
> think are appropriate comments. So here's a revised patch:
> 
> # 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       2010-08-06 08:09:08.000000000 +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 +1797,25 @@ 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) {
> +               /* we don't need to abort the connection if the socket
> +                * hasn't undergone a shutdown
> +                */
> +               if (transport->inet->sk_shutdown == 0)
> +                       return;
> +               dprintk("RPC:       %s: TCP_CLOSEd and sk_shutdown set
> to %d\n",
> +                       __func__, transport->inet->sk_shutdown);
> +       }
> +       if ((1 << state) & (TCPF_ESTABLISHED|TCPF_SYN_SENT)) {
> +               /* we don't need to abort the connection if the socket
> +                * hasn't undergone a shutdown
> +                */
> +               if (transport->inet->sk_shutdown == 0)
> +                       return;
> +               dprintk("RPC:       %s: ESTABLISHED/SYN_SENT "
> +                               "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>
> 

A weekend run with that patch applied to 2.6.34.2 was successful. As nobody has objected, what's the next step to getting it applied to the official source trees?

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

[Trond Myklebust]

On Mon, 2010-08-09 at 10:27 +0100, Andy Chittenden wrote:
> A weekend run with that patch applied to 2.6.34.2 was successful. As nobody has objected, what's the next step to getting it applied to the official source trees?

Please resend me a version with a cleaned up changelog entry. I can then
push it as a bugfix.

Cheers
  Trond

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

[Andy Chittenden]

> On Mon, 2010-08-09 at 10:27 +0100, Andy Chittenden wrote:
> > A weekend run with that patch applied to 2.6.34.2 was successful. As
> nobody has objected, what's the next step to getting it applied to the
> official source trees?
> 
> Please resend me a version with a cleaned up changelog entry. I can
> then
> push it as a bugfix.
> 
> Cheers
>   Trond

Thanks. I think this sums it up:

SUNRPC: fix NFS client over TCP hangs due to packet loss (Bug 16494)

When reusing a TCP connection, ensure that it's aborted if a previous shutdown attempt has been made on that connection so that the RPC over TCP recovery mechanism succeeds.

# 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       2010-08-06 08:09:08.000000000 +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 +1797,25 @@ 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) {
+               /* we don't need to abort the connection if the socket
+                * hasn't undergone a shutdown
+                */
+               if (transport->inet->sk_shutdown == 0)
+                       return;
+               dprintk("RPC:       %s: TCP_CLOSEd and sk_shutdown set to %d\n",
+                       __func__, transport->inet->sk_shutdown);
+       }
+       if ((1 << state) & (TCPF_ESTABLISHED|TCPF_SYN_SENT)) {
+               /* we don't need to abort the connection if the socket
+                * hasn't undergone a shutdown
+                */
+               if (transport->inet->sk_shutdown == 0)
+                       return;
+               dprintk("RPC:       %s: ESTABLISHED/SYN_SENT "
+                               "sk_shutdown set to %d\n",
+                               __func__, transport->inet->sk_shutdown);
+       }
        xs_abort_connection(xprt, transport);
 }

Signed-off-by: Andy Chittenden <andyc.bluearc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

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

[Joe Perches]

On Mon, 2010-08-09 at 10:27 +0100, Andy Chittenden wrote:

You really need to check your clock.
Mail sent in the year 2010?

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

[Andy C]

On 2018-06-19 22:56, Joe Perches wrote:
> On Mon, 2010-08-09 at 10:27 +0100, Andy Chittenden wrote:
>
> You really need to check your clock.
> Mail sent in the year 2010?
>
I didn't send it just now. I sent it on 2010-08-09 at 10:27. And I did 
receive a copy at that time. If I'm reading the headers correctly, 
something happened here:

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-- 
Andy