ath: Unable to remove station entry

[Michael Tokarev <mjt@tls.msk.ru>]

Hello.

Recently I bought a TP-Link TL-WN821N v3 802.11n USB adaptor,
and tried to use it as an access point for a small Wireless LAN.

It works fine so far, except of one issue.

Quite often to be really annoying, it stops working with the
following message in kernel log:

Jul  5 09:51:26 gnome vmunix: [133814.449408] ath: Unable to remove station entry for: 38:aa:3c:02:07:f1

after this, the interface is stuck, it can't be seen over WIFI,
and any attempt to do anything with it inside the host results
in more processes entering D state (initially right when this
happens, there's a kworker process in D state).

For example, `rmmod ath9k_htc' - which appears to be a topmost
module on the stack - results in rmmod entering D state, with
the following stack:

 rmmod           D 000000010266c10c     0 10684  10643 0x00000000
  ffffffff8148b020 0000000000000082 0000000000012400 ffff88012ae9d7d0
  ffff880114843fd8 ffff880114843fd8 ffff880114843fd8 ffff88012ae9d7d0
  0000000125aa5040 ffffffff8148b020 0000000000012400 ffff8801298cb500
 Call Trace:
  [<ffffffff81367a59>] ? __schedule+0x3a9/0x960
  [<ffffffff810558f0>] ? usleep_range+0x40/0x40
  [<ffffffff81368e38>] ? __mutex_lock_slowpath+0xc8/0x140
  [<ffffffff813689ba>] ? mutex_lock+0x1a/0x40
  [<ffffffffa025bc66>] ? ath9k_wmi_cmd+0xc6/0x200 [ath9k_htc]
  [<ffffffffa02614d8>] ? ath9k_regread+0x38/0x50 [ath9k_htc]
  [<ffffffffa0076849>] ? ath_hw_keyreset+0x59/0x220 [ath]
  [<ffffffffa0076a2d>] ? ath_key_delete+0x1d/0xdc [ath]
  [<ffffffffa025edc5>] ? ath9k_htc_set_key+0x85/0x130 [ath9k_htc]
  [<ffffffffa0230d19>] ? ieee80211_key_disable_hw_accel+0x89/0x130 [mac80211]
  [<ffffffffa0230ddc>] ? __ieee80211_key_destroy+0x1c/0x80 [mac80211]
  [<ffffffffa0231505>] ? ieee80211_free_keys+0x45/0x80 [mac80211]
  [<ffffffffa02233a7>] ? ieee80211_do_stop+0x1f7/0x5c0 [mac80211]
  [<ffffffff812d9f40>] ? dev_deactivate_many+0x1f0/0x240
  [<ffffffffa0223785>] ? ieee80211_stop+0x15/0x20 [mac80211]
  [<ffffffff812bc505>] ? __dev_close_many+0x85/0xd0
  [<ffffffff812bc638>] ? dev_close_many+0x98/0x110
  [<ffffffff812bc788>] ? rollback_registered_many+0xd8/0x250
  [<ffffffff812bc90e>] ? unregister_netdevice_many+0xe/0x60
  [<ffffffffa0222f00>] ? ieee80211_remove_interfaces+0xc0/0x100 [mac80211]
  [<ffffffffa0211096>] ? ieee80211_unregister_hw+0x46/0x110 [mac80211]
  [<ffffffffa02624c4>] ? ath9k_htc_disconnect_device+0x54/0xd0 [ath9k_htc]
  [<ffffffffa025b3a2>] ? ath9k_hif_usb_disconnect+0x52/0x150 [ath9k_htc]
  [<ffffffffa005dd52>] ? usb_unbind_interface+0x42/0x150 [usbcore]
  [<ffffffff81274546>] ? __device_release_driver+0x76/0xe0
  [<ffffffff81274bf0>] ? driver_detach+0xa0/0xb0
  [<ffffffff812743d0>] ? bus_remove_driver+0x70/0xc0
  [<ffffffffa005d7a6>] ? usb_deregister+0xa6/0xc0 [usbcore]
  [<ffffffffa0262d36>] ? ath9k_htc_exit+0x6/0x16 [ath9k_htc]
  [<ffffffff81080ee2>] ? sys_delete_module+0x132/0x260
  [<ffffffff8136a245>] ? page_fault+0x25/0x30
  [<ffffffff81371552>] ? system_call_fastpath+0x16/0x1b

followed by:

Jul  5 10:02:27 gnome vmunix: [134474.473451] ath: Unable to remove interface at idx: 0

(rmmod is stuck forever).

Now, in order to make the interface to work again, the only way I
found so far is to _reboot_ the machine.  For example, re-plugging
the USB cord does not help, because, as far as I can see, the driver
is in some weird state and can't initialize the new interface.

This is a 3.2.0-stable kernel (right now 3.2.46), x86-64 (amd64),
self-compiled, without additional patches.


There are a few references to this message on the 'net, including
one mentioning this very card (in russian) --

  http://forums.opensuse.org/p-russian/dhydhdhdhdhundhdhdh/1046-1077-1083-1077-1079-1086/469022-wifi-usb-tp-link-tl-wn821n.html

they claim the problem has been fixed for _some_ by upgrading the
BIOS on the motherboard.  Maybe this is actually related, because
as far as I can tell, this started happening _after_ I upgraded
BIOS on my motherboard, so it may be related to the bios changes.
I don't recall whenever I noticed this erratic behavour before I
upgraded BIOS.  Looking at the BIOS history, I don't see anything
interesting about USB in the changelog, except this:

 * Fixed issue with Fast Boot so USB devices still work under DOS
   if USB Optimization is enabled.

This is an intel atom-based D2500CC board, with the latest BIOS.
I had to update bios because of another issue which is now fixed,
but I can't go back to the old bios because the old one was too
old and current motherboard refuses to flash it.


What can be done to diagnose the problem?  I can give a more recent
kernel a try, but I'd love to see it fixed for a -stable kernel which
is used by several major distributions.  Also, the problem is not
easy to trigger, the system may work for a few days without issues
or may stop working in a few hours, irrespective of the load (f.e.
the above example at 09:51 was me awakening my android phone just
to see what time it is now, and it trying to connect/disconnect
to/from the default wifi network -- there were no other devices
using wifi at that time).

Thanks,

/mjt