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Message-ID: <20150917214758.GW21084@n2100.arm.linux.org.uk>
Date: Thu, 17 Sep 2015 22:47:58 +0100
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: Trond Myklebust <trond.myklebust@...marydata.com>
Cc: AnnaSchumaker <anna.schumaker@...app.com>, netdev@...r.kernel.org,
linux-nfs@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: NFS/TCP/IPv6 acting strangely in 4.2
On Thu, Sep 17, 2015 at 10:18:29AM -0400, Trond Myklebust wrote:
> Hi Russell,
>
> On Thu, 2015-09-17 at 14:57 +0100, Russell King - ARM Linux wrote:
> > On Fri, Sep 11, 2015 at 05:49:38PM +0100, Russell King - ARM Linux
> > wrote:
> > > Following that idea, I just tried the patch below, and it seems to
> > > work.
> > > I don't know whether it handles all cases after a call to
> > > kernel_connect(),
> > > but it stops the multiple connection attempts:
> > >
> > > 1 0.000000 armada388 -> n2100 TCP 1009→nfs [SYN] Seq=3794066539
> > > Win=28560 Len=0 MSS=1440 SACK_PERM=1 TSval=15712 TSecr=870317691
> > > WS=128
> > > 2 0.000414 n2100 -> armada388 TCP nfs→1009 [SYN, ACK]
> > > Seq=1884476522 Ack=3794066540 Win=28560 Len=0 MSS=1440 SACK_PERM=1
> > > TSval=870318939 TSecr=15712 WS=64
> > > 3 0.000787 armada388 -> n2100 TCP 1009→nfs [ACK] Seq=3794066540
> > > Ack=1884476523 Win=28672 Len=0 TSval=15712 TSecr=870318939
> > > 4 0.001304 armada388 -> n2100 NFS V3 ACCESS Call, FH:
> > > 0x905379cc, [Check: RD LU MD XT DL]
> > > 5 0.001566 n2100 -> armada388 TCP nfs→1009 [ACK] Seq=1884476523
> > > Ack=3794066660 Win=28608 Len=0 TSval=870318939 TSecr=15712
> > > 6 0.001640 armada388 -> n2100 NFS V3 ACCESS Call, FH:
> > > 0x905379cc, [Check: RD LU MD XT DL]
> > > 7 0.001866 n2100 -> armada388 TCP nfs→1009 [ACK] Seq=1884476523
> > > Ack=3794066780 Win=28608 Len=0 TSval=870318939 TSecr=15712
> > > 8 0.003070 n2100 -> armada388 NFS V3 ACCESS Reply (Call In 4),
> > > [Allowed: RD LU MD XT DL]
> > > 9 0.003415 armada388 -> n2100 TCP 1009→nfs [ACK] Seq=3794066780
> > > Ack=1884476647 Win=28672 Len=0 TSval=15712 TSecr=870318939
> > > 10 0.003592 armada388 -> n2100 NFS V3 ACCESS Call, FH:
> > > 0xe15fc9c9, [Check: RD LU MD XT DL]
> > > 11 0.004354 n2100 -> armada388 NFS V3 ACCESS Reply (Call In 6),
> > > [Allowed: RD LU MD XT DL]
> > > 12 0.004682 armada388 -> n2100 NFS V3 ACCESS Call, FH:
> > > 0xe15fc9c9, [Check: RD LU MD XT DL]
> > > 13 0.005365 n2100 -> armada388 NFS V3 ACCESS Reply (Call In 10),
> > > [Allowed: RD LU MD XT DL]
> > > 14 0.005701 armada388 -> n2100 NFS V3 GETATTR Call, FH:
> > > 0xe15fc9c9
> > > ...
> >
> > NFS people - any comments on this patch? Is it the correct way to
> > solve
> > this problem (please see the first message in this thread for the
> > problem.)
> > Without this patch, NFS is unusable as it tries to launch multiple
> > new
> > connections from the same port to the NFS server without giving the
> > NFS
> > server time to respond and establish the TCP connection.
>
> I agree that it addresses a real problem here, however there are a
> couple of issues with the patch itself:
>
> AFAICS, the 2 possible next states for SYN_SENT are TCP_ESTABLISHED and
> TCP_CLOSE, so if the connection attempt fails, this patch leaves the
> XPRT_CONNECTING flag set.
> There is also the issue that clearing XPRT_CONNECTING in TCP_FIN_WAIT1,
> TCP_CLOSE_WAIT and TCP_CLOSING could interfere with another connection
> attempt by canceling the XPRT_CONNECTING state.
>
> How about the following? It is based on your patch, but adds a check to
> ensure that xs_tcp_state_change() doesn't clear the 'connecting' state
> more than once (which could otherwise still happen in the TCP_CLOSE
> case).
This patch also seems to fix the problem I've been seeing.
Yes, I wasn't sure about my patch - I didn't spend much time properly
reading and understanding the sunrpc code, beyond analysing what was
going on to cause the problem and deciding on a way to stop it happening.
I really wasn't sure that clearing the connecting flag everywhere I did
was the right thing, which is why I didn't send the patch properly
dressed up.
> 8<-------------------------------------------------------------------
> >From 4dbfdebbc09982a9248866f8256549456e2b2efd Mon Sep 17 00:00:00 2001
> From: Trond Myklebust <trond.myklebust@...marydata.com>
> Date: Wed, 16 Sep 2015 23:43:17 -0400
> Subject: [PATCH] SUNRPC: Ensure that we wait for connections to complete
> before retrying
>
> Commit 718ba5b87343, moved the responsibility for unlocking the socket to
> xs_tcp_setup_socket, meaning that the socket will be unlocked before we
> know that it has finished trying to connect. The following patch is based on
> an initial patch by Russell King to ensure that we delay clearing the
> XPRT_SOCK_CONNECTING flag until we either know that we failed to initiate
> a connection attempt, or the connection attempt itself failed.
>
> Fixes: 718ba5b87343 ("SUNRPC: Add helpers to prevent socket create from racing")
> Reported-by: Russell King <linux@....linux.org.uk>
Reported-by: Russell King <rmk+kernel@....linux.org.uk>
Tested-by: Russell King <rmk+kernel@....linux.org.uk>
Thanks.
> Signed-off-by: Trond Myklebust <trond.myklebust@...marydata.com>
> ---
> include/linux/sunrpc/xprtsock.h | 3 +++
> net/sunrpc/xprtsock.c | 11 ++++++++---
> 2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/sunrpc/xprtsock.h b/include/linux/sunrpc/xprtsock.h
> index 7591788e9fbf..357e44c1a46b 100644
> --- a/include/linux/sunrpc/xprtsock.h
> +++ b/include/linux/sunrpc/xprtsock.h
> @@ -42,6 +42,7 @@ struct sock_xprt {
> /*
> * Connection of transports
> */
> + unsigned long sock_state;
> struct delayed_work connect_worker;
> struct sockaddr_storage srcaddr;
> unsigned short srcport;
> @@ -76,6 +77,8 @@ struct sock_xprt {
> */
> #define TCP_RPC_REPLY (1UL << 6)
>
> +#define XPRT_SOCK_CONNECTING 1U
> +
> #endif /* __KERNEL__ */
>
> #endif /* _LINUX_SUNRPC_XPRTSOCK_H */
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index 7be90bc1a7c2..5bac27983e2a 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -1435,6 +1435,7 @@ out:
> static void xs_tcp_state_change(struct sock *sk)
> {
> struct rpc_xprt *xprt;
> + struct sock_xprt *transport;
>
> read_lock_bh(&sk->sk_callback_lock);
> if (!(xprt = xprt_from_sock(sk)))
> @@ -1446,13 +1447,12 @@ static void xs_tcp_state_change(struct sock *sk)
> sock_flag(sk, SOCK_ZAPPED),
> sk->sk_shutdown);
>
> + transport = container_of(xprt, struct sock_xprt, xprt);
> trace_rpc_socket_state_change(xprt, sk->sk_socket);
> switch (sk->sk_state) {
> case TCP_ESTABLISHED:
> spin_lock(&xprt->transport_lock);
> if (!xprt_test_and_set_connected(xprt)) {
> - struct sock_xprt *transport = container_of(xprt,
> - struct sock_xprt, xprt);
>
> /* Reset TCP record info */
> transport->tcp_offset = 0;
> @@ -1461,6 +1461,8 @@ static void xs_tcp_state_change(struct sock *sk)
> transport->tcp_flags =
> TCP_RCV_COPY_FRAGHDR | TCP_RCV_COPY_XID;
> xprt->connect_cookie++;
> + clear_bit(XPRT_SOCK_CONNECTING, &transport->sock_state);
> + xprt_clear_connecting(xprt);
>
> xprt_wake_pending_tasks(xprt, -EAGAIN);
> }
> @@ -1496,6 +1498,9 @@ static void xs_tcp_state_change(struct sock *sk)
> smp_mb__after_atomic();
> break;
> case TCP_CLOSE:
> + if (test_and_clear_bit(XPRT_SOCK_CONNECTING,
> + &transport->sock_state))
> + xprt_clear_connecting(xprt);
> xs_sock_mark_closed(xprt);
> }
> out:
> @@ -2179,6 +2184,7 @@ static int xs_tcp_finish_connecting(struct rpc_xprt *xprt, struct socket *sock)
> /* Tell the socket layer to start connecting... */
> xprt->stat.connect_count++;
> xprt->stat.connect_start = jiffies;
> + set_bit(XPRT_SOCK_CONNECTING, &transport->sock_state);
> ret = kernel_connect(sock, xs_addr(xprt), xprt->addrlen, O_NONBLOCK);
> switch (ret) {
> case 0:
> @@ -2240,7 +2246,6 @@ static void xs_tcp_setup_socket(struct work_struct *work)
> case -EINPROGRESS:
> case -EALREADY:
> xprt_unlock_connect(xprt, transport);
> - xprt_clear_connecting(xprt);
> return;
> case -EINVAL:
> /* Happens, for instance, if the user specified a link
> --
> 2.4.3
>
> --
> Trond Myklebust
> Linux NFS client maintainer, PrimaryData
> trond.myklebust@...marydata.com
>
>
>
--
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.
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