read of file on nfs3 mounted fs fails with udp option

[Ariel Glenn]

Server: 2.6.32-27-server #49-Ubuntu SMP Thu Dec 2 02:05:21 UTC 2010 x86_64 GNU/Linux
Client: 2.6.32-32-server #62-Ubuntu SMP Wed Apr 20 22:07:43 UTC 2011 x86_64 GNU/Linux
nfs-kernel-server: 1.2.0-4ubuntu4.1

A specific file can be read/copied locally, but not via nfs with the udp option set. If the server is lucid and the client is lucid I don't see this error, and using tcp instead of udp works as well. (This has to do with the specific contents of the file, as a copy tested on other hardy servers with other lucid clients shows the same result.)

I'd attach the file here but it's quite large: 657427216 bytes.

The failure to read produces "nfs: server XXX not responding, timed out" in the syslog on the client, and the message "Input/output error" in the terminal window.

The read failure occurs at a very interesting place:
root@XXX:~# od -c /mnt/test/test.gz | tail
od: /mnt/test/test.gz: read error: Input/output error
2077777560 210 016 \b 305 031 323 016 026 264 6 ~ - 020 006 273 1
2077777600 341 F 327 002 B 304 1 u J v \f > 037 314 362 321
2077777620 d x 261 \ 024 313 031 353 \t 242 X @ j 305 356 \b
2077777640 303 301 ' 023 215 314 > ] : 314 030 016 016 k 242 _
2077777660 3 212 211 < 021 < 036 X 234 226 364 271 361 321 ` [
2077777700 a E 343 / 3 222 260 Z 215 243 1 242 214 264 206 207
2077777720 364 X 334 Q 217 275 : r z 314 004 360 [ 204 I /
2077777740 ' 035 233 340 \r j S # h 321 267 307 361 336 330
2077777760 202 E 253 020 y 006 g 342 361 325 240 215 6 026 250 213
2100000000

I guess it's some sort of overflow error, it would be nice to know that the offending code is actually gone from lucid instead of in a slightly different place in the code path waiting to be triggered by different file contents.