Bug#626284: Bogus UDP Fragmentation Offload packet generation
The new UFO software fallback path fails under certain conditions with NFS
and causes partial connectivity loss due to generation of UFO packets smaller
than the MTU, which are then discarded by the software fallback path.
This bug is present in all longterm 2.6.32.x kernels up to and including
188.8.131.52 and in all Debian 2.6.32 kernels up to and including 2.6.32-31.
It was fixed upstream in 184.108.40.206. Upstream commit ID is
How to reproduce: copy a large file to an NFS mount with UFO enabled and
going through the software fallback path, e.g. on a KVM guest with virtio-net
and qdev device syntax:
-device virtio-net-pci,netdev=tap1,mac=ab:cd:ef:01:23:45 \
All NFS mounts immediately stall and processes go into D state,
stuck on nfs_wait_bit_uninterruptible. There is no further communication
between the client and the server.