NFS/TCP/IPv6 acting strangely in 4.2

[Trond Myklebust]

On Thu, Sep 17, 2015 at 5:47 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> 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 at primarydata.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 at arm.linux.org.uk>
>
> Reported-by: Russell King <rmk+kernel at arm.linux.org.uk>
> Tested-by: Russell King <rmk+kernel at arm.linux.org.uk>
>

Thanks Russell!