8.2.1 WPA testing

Chris Ball cjb at laptop.org
Sun Mar 1 19:08:26 EST 2009


I've been working on trying to quantify the difference in WPA behavior
between 8.2.0 and 8.2.1.  My test setup involves attempting to connect
to a WPA AP inside Sugar, performing suspend/resume, and trying again.
A success involves Sugar reporting "Connected", and a failure involves
Sugar asking for the WPA key again -- when this happened, I clicked
cancel, suspended, and began the next iteration.

Failures leave the string "Activation (eth0/wireless): disconnected
during association, asking for new key" in /var/log/messages.  A second
type of failure is seen only on 8.2.0, namely "Unhandled network
capabilities 10000001"; this bug is fixed in 8.2.1, and was not included
in the totals below.

Machine 1, build 801:
  50 iterations:
    success:  23 (46% of attempts successful)
    failure:  27

Machine 2, build 801 with 767 kernel and wireless firmware:
  50 iterations:
    success:  30 (60% of attempts successful)
    failure:  20

Machine 3, build 767:
  50 iterations:
    success:  32 (64% of attempts successful)
    failure:  18

  For this particular bug (being asked to re-enter the WPA passphrase
  at connection time), with the particular WPA access points at 1cc, we
  already had sporadic failures as of 8.2.0.  8.2.1 appears to make them
  slightly worse, perhaps suggesting a widening of a race condition in
  the newer driver or wireless firmware.  We already know installing
  WPA keys to be time-critical:  see relevant recent commits ¹ and ².

  Since the 8.2.0 behavior is seen on an 8.2.1 build with kernel and
  firmware downgraded, we can rule out changes to Sugar/NetworkManager
  as having caused the 8.2.1 regression.

  We should not claim reliable WPA support in 8.2.1.  Since we have
  other WPA fixes available in the 8.2.1 kernel (such as ³) the new
  kernel is perhaps still a better 8.2.1 candidate than the old one.
  In either case, we should document the workaround of "if you've
  previously typed in the WPA passphrase and you're asked for it
  again, you should click Cancel and attempt to reconnect", which
  usually works.  Also, note that this bug is not the only reported
  failure around WPA, although it is the bug that seems to affect all
  access points (rather than just individual ones).

  There's a large delta between the 8.2.x kernel of 2.6.25 and the
  current upstream 2.6.29 work; further effort at making WPA reliable
  would probably be better-focused on the upstream kernel rather than
  our 2.6.25 snapshot.

Further comments/thoughts welcome!

- Chris.

¹:  http://dev.laptop.org/git?p=olpc-2.6;a=commit;h=f10b654367d7065d50e7d5e3649933453cea3102
²:  http://dev.laptop.org/git?p=olpc-2.6;a=commit;h=b0a7455f0ba53774a30a7af6505816855488cc40
³:  http://dev.laptop.org/git?p=olpc-2.6;a=commit;h=011dd3f2d6fbd75ae2aacdcf8f99ebeddf814227

Chris Ball   <cjb at laptop.org>

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