CFT/CFR, possible fix for ifconfig scan hang

[Bernhard Schmidt]

Hi,

no objections so far. If non arise till this weekend, I going to commit this.

On Monday 27 December 2010 20:24:36 Bernhard Schmidt wrote:
> Hi,
> 
> I recently received some complains about the infamous 'ifconfig scan hang'
> issue again. Finally looking into that I noticed a bunch of inconsistences,
> the most obvious one is that ifconfig(8) is talking about doing a
>  background scan by default, which is simply not true according to the
>  implementation.
> 
> Anyways.. the generic use-case which triggers the 'hang' is, if 'ifconfig
> scan' is called while a scan is already in progress, net80211 will not
>  start a new one which means that no scan flags are updated, though,
>  ifconfig will loop until it receives a notification about the scan being
>  done. This does always happen after an 'ifconfig up', because net80211
>  will move the VAP into scan state by default, with the scan flags set in
>  such a way that a scan is done until there is something to connect to.
>  This also means that no notifications about the scan being done are sent
>  to upper layers, because the scan is not finished..
> 
> If we successfully moved from scan to run state, how so ever, and now want
>  to call 'ifconfig scan' we're faced with another issue. Doing a scan while
>  being associated means we have to move off our current channel, to do this
>  without loosing any imported frames/information, we make use of the power
>  save feature. Now if we want to send any traffic while doing the scan, the
>  scan is temporary suspended, frames are sent, then the scan is restarted
>  after receiving a beacon and there is no frame to send. For this to work
>  though, we need to actually request a background scan so appropriate flags
>  are set and the scan is actually restarted. Without this, we hang until
>  the bgscan timer fires of at that next bgscanintval.
> 
> I have a patch available which addresses both of the issues. It requests a
> background scan by default and also honors the return value of
> start_scan_locked():
> - for head
> http://techwires.net/~bschmidt/scan_hang_head.diff
> - for 8-stable/8.2-*:
> http://techwires.net/~bschmidt/scan_hang_stable.diff
> 
> Please test and let me know if it works, or not.
> 
> Thanks
> 

-- 
Bernhard