8.0-RC1 NFS client timeout issue
Rick Macklem
rmacklem at uoguelph.ca
Wed Oct 28 20:31:25 UTC 2009
First off, I know that cross posting is evil, but I wanted to try
and make sure developers saw it.
On Tue, 27 Oct 2009, Olaf Seibert wrote:
> I see an annoying behaviour with NFS over TCP. It happens both with nfs
> and newnfs. This is with FreeBSD/amd64 8.0-RC1 as client. The server is
> some Linux or perhaps Solaris, I'm not entirely sure.
>
> After trying to find something in packet traces, I think I have found
> something.
>
> The scenario seems to be as follows. Sorry for the width of the lines.
>
>
> No. Time Source Destination Protocol Info
> 2296 2992.216855 xxx.xxx.31.43 xxx.xxx.16.142 NFS V3 LOOKUP Call (Reply In 2297), DH:0x3819da36/w
> 2297 2992.217107 xxx.xxx.16.142 xxx.xxx.31.43 NFS V3 LOOKUP Reply (Call In 2296) Error:NFS3ERR_NOENT
> 2298 2992.217141 xxx.xxx.31.43 xxx.xxx.16.142 NFS V3 LOOKUP Call (Reply In 2299), DH:0x170cb16a/bin
> 2299 2992.217334 xxx.xxx.16.142 xxx.xxx.31.43 NFS V3 LOOKUP Reply (Call In 2298), FH:0x61b8eb12
> 2300 2992.217361 xxx.xxx.31.43 xxx.xxx.16.142 NFS V3 ACCESS Call (Reply In 2301), FH:0x61b8eb12
> 2301 2992.217582 xxx.xxx.16.142 xxx.xxx.31.43 NFS V3 ACCESS Reply (Call In 2300)
> 2302 2992.217605 xxx.xxx.31.43 xxx.xxx.16.142 NFS V3 LOOKUP Call (Reply In 2303), DH:0x61b8eb12/w
> 2303 2992.217860 xxx.xxx.16.142 xxx.xxx.31.43 NFS V3 LOOKUP Reply (Call In 2302) Error:NFS3ERR_NOENT
> 2304 2992.318770 xxx.xxx.31.43 xxx.xxx.16.142 TCP 934 > nfs [ACK] Seq=238293 Ack=230289 Win=8192 Len=0 TSV=86492342 TSER=12393434
> 2306 3011.537520 xxx.xxx.16.142 xxx.xxx.31.43 NFS V3 GETATTR Reply (Call In 2305) Directory mode:2755 uid:4100 gid:4100
> 2307 3011.637744 xxx.xxx.31.43 xxx.xxx.16.142 TCP 934 > nfs [ACK] Seq=238429 Ack=230405 Win=8192 Len=0 TSV=86511662 TSER=12395366
> 2308 3371.534980 xxx.xxx.16.142 xxx.xxx.31.43 TCP nfs > 934 [FIN, ACK] Seq=230405 Ack=238429 Win=49232 Len=0 TSV=12431366 TSER=86511662
>
> The server decides, for whatever reason, to terminate the
> connection and sends a FIN.
>
> 2309 3371.535018 xxx.xxx.31.43 xxx.xxx.16.142 TCP 934 > nfs [ACK] Seq=238429 Ack=230406 Win=8192 Len=0 TSV=86871578 TSER=12431366
>
> Client acknowledges this,
>
> 2310 3375.379693 xxx.xxx.31.43 xxx.xxx.16.142 NFS V3 ACCESS Call, FH:0x008002a2
>
> but tries to sneak in another call anyway. [A]
>
Probably not the best behaviour, but I think it is technically allowed by
TCP. (My TCP is very rusty, but I think the socket should be in
TCPS_CLOSE_WAIT at this point and the BSD code will have called
socantrcvmore(), but not socantsndmore().)
> 2311 3375.474788 xxx.xxx.16.142 xxx.xxx.31.43 TCP nfs > 934 [ACK] Seq=230406 Ack=238569 Win=49232 Len=0 TSV=12431760 TSER=86875423
>
> Server ACKs but doesn't send anything else... [B]
>
> Time passes...
>
This is where it seems interesting. It looks to me like the socket upcall
for receiving the FIN would have happened before this point, setting the
ct_error.re_status to RPC_CANTRECV, but the code in clnt_vc_call() doesn't
check for this. (It does check for it happening during and after the
sosend(), but not before it, from what I can see.)
>
> [B] would be a bug of the server in my opinion. If it ACKs a call, it
> should send a reply. And if it can't, it shouldn't.
>
I'll leave this one for the TCP wizzards. I'm not sure what the
correct behaviour is when data is received on a connection. (I think
it is waiting for a FIN from the client side at this point.)
If you could try the following patch and see if it helps, that would be
appreciated, rick
ps: I'll try to reproduce the situation here, but I'm not sure if I can.
--- rpc/clnt_vc.c.sav 2009-10-28 15:44:20.000000000 -0400
+++ rpc/clnt_vc.c 2009-10-28 15:49:57.000000000 -0400
@@ -413,6 +413,19 @@
cr->cr_xid = xid;
mtx_lock(&ct->ct_lock);
+ /*
+ * Check to see if the other end has already started to close down
+ * the connection. If it happens after this point, it will be
+ * detected below, when cr->cr_error is checked.
+ */
+ if (ct->ct_error.re_status == RPC_CANTRECV) {
+ if (errp != &ct->ct_error) {
+ errp->re_errno = ct->ct_error.re_errno;
+ errp->re_status = RPC_CANTRECV;
+ }
+ stat = RPC_CANTRECV;
+ goto out;
+ }
TAILQ_INSERT_TAIL(&ct->ct_pending, cr, cr_link);
mtx_unlock(&ct->ct_lock);
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