Bug 163573 - [ath] hostap mode TX buffer hang
Summary: [ath] hostap mode TX buffer hang
Status: Open
Alias: None
Product: Base System
Classification: Unclassified
Component: wireless (show other bugs)
Version: Unspecified
Hardware: Any Any
: Normal Affects Only Me
Assignee: freebsd-wireless (Nobody)
Depends on:
Reported: 2011-12-23 19:20 UTC by Adrian Chadd
Modified: 2018-05-28 19:44 UTC (History)
0 users

See Also:


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Description Adrian Chadd freebsd_committer 2011-12-23 19:20:07 UTC
When testing 802.11n hostap mode, the TX side still occasionally hangs.

This is again due to the "busy" buffer management code being slightly wrong, allowing a "busy" buffer to stay busy and eventually clogging up the free TX buffer ring.

This occurs with IEEE80211_SUPPORT_TDMA, as the busy buffer code isn't included otherwise. (It should be though, due to how the MAC behaves. But that's a different problem.)

The relevant output from "sysctl dev.ath.0.txagg=1" is:

HW TXQ 0: axq_depth=2, axq_aggr_depth=2
HW TXQ 1: axq_depth=0, axq_aggr_depth=0
HW TXQ 2: axq_depth=0, axq_aggr_depth=0
HW TXQ 3: axq_depth=0, axq_aggr_depth=0
HW TXQ 8: axq_depth=0, axq_aggr_depth=0
Busy: 0
Total TX buffers: 1; Total TX buffers busy: 1

. the fact that there's only 1 total buffer in the free list, and that one is busy, indicates that things were going pear shaped.

Also, athstats can be helpful:

# athstats | grep tx
294          tx stopped 'cuz no xmit buffer


Not yet.
How-To-Repeat: Just exchange a bunch of traffic whilst in a lossy 802.11 network. It should eventually get angry and stop transmitting. ifconfig wlan0 down / up will flush the TX buffer queue.

Enable both 802.11 and TDMA in the kernel configuration file (ATH_ENABLE_11N and IEEE80211_SUPPORT_TDMA.) Configure the unit as a hostap - in non-hostap mode, the interface resets will cause the TX buffer queue to be flushed.

Sit back and watch the fireworks.
Comment 1 Adrian Chadd freebsd_committer 2011-12-23 19:22:34 UTC
Responsible Changed
From-To: freebsd-bugs->freebsd-wireless

Over to -wireless.
Comment 2 Eitan Adler freebsd_committer freebsd_triage 2018-05-28 19:44:07 UTC
batch change:

For bugs that match the following
-  Status Is In progress 
- Untouched since 2018-01-01.
- Affects Base System OR Documentation


Reset to open status.

I did a quick pass but if you are getting this email it might be worthwhile to double check to see if this bug ought to be closed.