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Message-ID: <ABFC24E4C13D81489F7F624E14891C8607DDF8D3BF@uk-ex-mbx1.terastack.bluearc.com> Date: Wed, 28 Jul 2010 08:08:53 +0100 From: Andy Chittenden <andyc@...earc.com> To: Chuck Lever <chuck.lever@...cle.com>, Eric Dumazet <eric.dumazet@...il.com> CC: "Linux Kernel Mailing List (linux-kernel@...r.kernel.org)" <linux-kernel@...r.kernel.org>, Trond Myklebust <trond.myklebust@....uio.no>, netdev <netdev@...r.kernel.org>, Linux NFS Mailing List <linux-nfs@...r.kernel.org> Subject: RE: nfs client hang > I don't see an xs_error_report() call here, which would confirm that the socket took a trip through tcp_disconnect(). From my reading of tcp_disconnect(), it calls sk->sk_error_report(sk) unconditionally so as there's no xs_error_report(), that surely means the exact opposite: tcp_disconnect() wasn't called. If it's not called, sk_shutdown is not cleared. And my revised tracing confirmed that it was set to SEND_SHUTDOWN. -- Andy, BlueArc Engineering -----Original Message----- From: Chuck Lever [mailto:chuck.lever@...cle.com] Sent: 27 July 2010 18:29 To: Eric Dumazet Cc: Andy Chittenden; Linux Kernel Mailing List (linux-kernel@...r.kernel.org); Trond Myklebust; netdev; Linux NFS Mailing List Subject: Re: nfs client hang Add CC: linux-nfs@...r.kernel.org On 07/27/10 08:21 AM, Eric Dumazet wrote: > Le mardi 27 juillet 2010 à 11:53 +0100, Andy Chittenden a écrit : >>>>> IE the client starts a connection and then closes it again without sending data. >>>> Once this happens, here's some rpcdebug info for the rpc module using 2.6.34.1 kernel: >>>> >>>> ... lots of the following nfsv3 WRITE requests: >>>> [ 7670.026741] 57793 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026759] 57794 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026778] 57795 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026797] 57796 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026815] 57797 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026834] 57798 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026853] 57799 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026871] 57800 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026890] 57801 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7670.026909] 57802 0001 -11 ffff88012e32b000 (null) 0 ffffffffa03beb10 nfsv3 WRITE a:call_reserveresult q:xprt_backlog >>>> [ 7680.520042] RPC: worker connecting xprt ffff88013e62d800 via tcp to 10.1.6.102 (port 2049) >>>> [ 7680.520066] RPC: ffff88013e62d800 connect status 99 connected 0 sock state 7 >>>> [ 7680.520074] RPC: 33550 __rpc_wake_up_task (now 4296812426) >>>> [ 7680.520079] RPC: 33550 disabling timer >>>> [ 7680.520084] RPC: 33550 removed from queue ffff88013e62db20 "xprt_pending" >>>> [ 7680.520089] RPC: __rpc_wake_up_task done >>>> [ 7680.520094] RPC: 33550 __rpc_execute flags=0x1 >>>> [ 7680.520098] RPC: 33550 xprt_connect_status: retrying >>>> [ 7680.520103] RPC: 33550 call_connect_status (status -11) >>>> [ 7680.520108] RPC: 33550 call_transmit (status 0) >>>> [ 7680.520112] RPC: 33550 xprt_prepare_transmit >>>> [ 7680.520118] RPC: 33550 rpc_xdr_encode (status 0) >>>> [ 7680.520123] RPC: 33550 marshaling UNIX cred ffff88012e002300 >>>> [ 7680.520130] RPC: 33550 using AUTH_UNIX cred ffff88012e002300 to wrap rpc data >>>> [ 7680.520136] RPC: 33550 xprt_transmit(32920) >>>> [ 7680.520145] RPC: xs_tcp_send_request(32920) = -32 >>>> [ 7680.520151] RPC: xs_tcp_state_change client ffff88013e62d800... >>>> [ 7680.520156] RPC: state 7 conn 0 dead 0 zapped 1 >> >>> I changed that debug to output sk_shutdown too. That has a value of 2 >>> (IE SEND_SHUTDOWN). Looking at tcp_sendmsg(), I see this: >> >>> err = -EPIPE; >>> if (sk->sk_err || (sk->sk_shutdown& SEND_SHUTDOWN)) >>> goto out_err; >> >>> which correlates with the trace "xs_tcp_send_request(32920) = -32". So, >>> this looks like a problem in the sockets/tcp layer. The rpc layer issues >>> a shutdown and then reconnects using the same socket. So either >>> sk_shutdown needs zeroing once the shutdown completes or should be >>> zeroed on subsequent connect. The latter sounds safer. >> This patch for 2.6.34.1 fixes the issue: >> >> --- /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 @@ >> 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. >> */ >> >> As I mentioned in my first message, we first saw this issue in 2.6.32 as supplied by debian (linux-image-2.6.32-5-amd64 Version: 2.6.32-17). It looks like the same patch would fix the problem there too. >> > > CC netdev > > This reminds me a similar problem we had in the past, fixed with commit > 1fdf475a (tcp: tcp_disconnect() should clear window_clamp) > > But tcp_disconnect() already clears sk->sk_shutdown > > If NFS calls tcp_disconnect(), then shutdown(), there is a problem. If tcp_disconnect() was called at some point, I would expect to see a message from xs_error_report() in the debugging output. Perhaps tcp_disconnect() is not being invoked at all? > Maybe xs_tcp_shutdown() should make some sanity tests ? > > Following sequence is legal, and your patch might break it. > > fd = socket(...); > shutdown(fd, SHUT_WR); > ... > connect(fd, ...); I looked closely at some of Andy's debugging output from the linux-kernel mailing list archive. I basically agree that the network layer is returning -EPIPE from tcp_sendmsg(), which the RPC client logic does not expect. But it's not clear to me how it gets into this state. > [ 7728.520042] RPC: worker connecting xprt ffff88013e62d800 via tcp to 10.1.6.102 (port 2049) > [ 7728.520093] RPC: ffff88013e62d800 connect status 115 connected 0 sock state 2 "sock state 2" => sk->sk_state == TCP_SYN_SENT > [ 7728.520884] RPC: xs_tcp_state_change client ffff88013e62d800... > [ 7728.520889] RPC: state 1 conn 0 dead 0 zapped 1 "state 1" => sk->sk_state == TCP_ESTABLISHED RPC client wakes up this RPC task now that the connection is established. > [ 7728.520896] RPC: 33550 __rpc_wake_up_task (now 4296824426) > [ 7728.520900] RPC: 33550 disabling timer > [ 7728.520906] RPC: 33550 removed from queue ffff88013e62db20 "xprt_pending" > [ 7728.520912] RPC: __rpc_wake_up_task done > [ 7728.520932] RPC: 33550 __rpc_execute flags=0x1 > [ 7728.520937] RPC: 33550 xprt_connect_status: retrying > [ 7728.520942] RPC: 33550 call_connect_status (status -11) The awoken RPC task's status is -EAGAIN, which prevents a reconnection attempt. > [ 7728.520947] RPC: 33550 call_transmit (status 0) > [ 7728.520951] RPC: 33550 xprt_prepare_transmit > [ 7728.520957] RPC: 33550 rpc_xdr_encode (status 0) > [ 7728.520962] RPC: 33550 marshaling UNIX cred ffff88012e002300 > [ 7728.520969] RPC: 33550 using AUTH_UNIX cred ffff88012e002300 to wrap rpc data > [ 7728.520976] RPC: 33550 xprt_transmit(32920) RPC client encodes the request and attempts to send it. > [ 7728.520984] RPC: xs_tcp_send_request(32920) = -32 Network layer says -EPIPE, for some reason. RPC client calls kernel_sock_shutdown(SHUT_WR). > [ 7728.520997] RPC: xs_tcp_state_change client ffff88013e62d800... > [ 7728.521007] RPC: state 4 conn 1 dead 0 zapped 1 "state 4" => sk->sk_state == TCP_FIN_WAIT1 The RPC client sets up a linger timeout. > [ 7728.521013] RPC: 33550 call_status (status -32) > [ 7728.521018] RPC: 33550 call_bind (status 0) > [ 7728.521023] RPC: 33550 call_connect xprt ffff88013e62d800 is not connected > [ 7728.521028] RPC: 33550 xprt_connect xprt ffff88013e62d800 is not connected > [ 7728.521035] RPC: 33550 sleep_on(queue "xprt_pending" time 4296824426) > [ 7728.521040] RPC: 33550 added to queue ffff88013e62db20 "xprt_pending" > [ 7728.521045] RPC: 33550 setting alarm for 60000 ms RPC client puts this RPC task to sleep. > [ 7728.521439] RPC: xs_tcp_state_change client ffff88013e62d800... > [ 7728.521444] RPC: state 5 conn 0 dead 0 zapped 1 "state 5" => sk->sk_state == TCP_FIN_WAIT2 > [ 7728.521602] RPC: xs_tcp_state_change client ffff88013e62d800... > [ 7728.521608] RPC: state 7 conn 0 dead 0 zapped 1 > [ 7728.521612] RPC: disconnected transport ffff88013e62d800 "state 7" => sk->sk_state == TCP_CLOSE The RPC client marks the socket closed. and the linger timeout is cancelled. At this point, sk_shutdown should be set to zero, correct? I don't see an xs_error_report() call here, which would confirm that the socket took a trip through tcp_disconnect(). > [ 7728.521617] RPC: 33550 __rpc_wake_up_task (now 4296824426) > [ 7728.521621] RPC: 33550 disabling timer > [ 7728.521626] RPC: 33550 removed from queue ffff88013e62db20 "xprt_pending" > [ 7728.521631] RPC: __rpc_wake_up_task done RPC client wakes up the RPC task. Meanwhile... > [ 7728.521636] RPC: xs_tcp_state_change client ffff88013e62d800... > [ 7728.521641] RPC: state 7 conn 0 dead 0 zapped 1 > [ 7728.521645] RPC: disconnected transport ffff88013e62d800 > [ 7728.521649] RPC: xs_tcp_data_ready... ... network layer calls closed socket's data_ready method... while the awoken RPC task gets underway. > [ 7728.521662] RPC: 33550 __rpc_execute flags=0x1 > [ 7728.521666] RPC: 33550 xprt_connect_status: retrying > [ 7728.521671] RPC: 33550 call_connect_status (status -11) The awoken RPC task's status is -EAGAIN, which prevents a reconnection attempt, even though there is no established connection. RPC client barrels on to send the request again. > [ 7728.521675] RPC: 33550 call_transmit (status 0) > [ 7728.521679] RPC: 33550 xprt_prepare_transmit > [ 7728.521683] RPC: 33550 rpc_xdr_encode (status 0) > [ 7728.521688] RPC: 33550 marshaling UNIX cred ffff88012e002300 > [ 7728.521694] RPC: 33550 using AUTH_UNIX cred ffff88012e002300 to wrap rpc data > [ 7728.521699] RPC: 33550 xprt_transmit(32920) > [ 7728.521704] RPC: xs_tcp_send_request(32920) = -32 RPC client attempts to send again, gets -EPIPE, and calls kernel_sock_shutdown(SHUT_WR). If there is no connection established, the RPC client expects -ENOTCONN, in which case it will attempt to reconnect here. > [ 7728.521709] RPC: xs_tcp_state_change client ffff88013e62d800... > [ 7728.521714] RPC: state 7 conn 0 dead 0 zapped 1 > [ 7728.521718] RPC: disconnected transport ffff88013e62d800 "state 7" => sk->sk_state == TCP_CLOSE Following this, the RPC client attempts to retransmit the request repeatedly, but the socket remains in the TCP_CLOSE state.
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