[Bugme-new] [Bug 33972] New: Bogus UDP Fragmentation Offload packet generation

bugzilla-daemon at bugzilla.kernel.org bugzilla-daemon at bugzilla.kernel.org
Tue Apr 26 04:46:06 PDT 2011


https://bugzilla.kernel.org/show_bug.cgi?id=33972

           Summary: Bogus UDP Fragmentation Offload packet generation
           Product: Networking
           Version: 2.5
    Kernel Version: 2.6.32.x
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: IPV4
        AssignedTo: shemminger at linux-foundation.org
        ReportedBy: tgr.kb at moo.pl
        Regression: Yes


Created an attachment (id=55552)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=55552)
udp: Fix bogus UFO 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.

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 \
-netdev type=tap,id=tap1,ifname=tap1

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.

It has been fixed in 2.6.35-rc4 by Herbert Xu (patch for net/ipv4/ip_output.c
attached). However, it's still not in 2.6.32.x longterm (as of 2.6.32.39).

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