WARNING: at net/mac80211/ieee80211_rate.h:159 rate_lowest_index()
Hi,
the warning in $subj can pop up in the following scenario:
- iwconfig wlan0 mode ad-hoc; ifconfig wlan0 up
- a frame arrives from an unknown station which triggers ieee80211_ibss_sta_add() (called from prepare_for_handlers())
In this case, we create a new sta entry, fill in supp_rates field, initialize rate_control algo, and insert this sta entry into the list.
The problem is the assignment for supp_rates:
sta->supp_rates[local->hw.conf.channel->band] =
sdata->u.sta.supp_rates_bits[local->hw.conf.channel->band];
because sdata->u.sta.supp_rates_bits is set only when we actually join an ibss, which is not the case in this scenario; so we assign zero here. Then, the code in rate_control_pid_rate_init() calls rate_lowest_index() for some reason, and since no supported rate is found, this warning is issued.
The question is how sta->supp_rates should be initialized:
- we could initialize it to our sta's rates, but then we could probably transmit to a station at unsupported rate
- add new ibss station only on received beacon, not on a data frame; currently, beacons are ignored for this purpose (they just update the bss list later on)
- something else (like 1Mbps only)?
As soon as we do sta_join_ibss(), this warning won't happen again.
Note that once we have sta entry (in our ibss), we will update its supported rates based on beacons it sends (in rx_bss_info()).
Any thoughts?
Regards,
Vlado
Quoted 6 lines · On Tuesday 29 April 2008 18:01:22 Vladimir Koutny wrote:
Hi,
the warning in $subj can pop up in the following scenario:- iwconfig wlan0 mode ad-hoc; ifconfig wlan0 up
- a frame arrives from an unknown station which triggersieee80211_ibss_sta_add()(called fromprepare_for_handlers())
yep, i have seen this warning too, just didn't get around to look into it...
Quoted 15 lines
In this case, we create a new sta entry, fill in
supp_ratesfield, initializerate_controlalgo, and insert this sta entry into the list.The problem is the assignment for
supp_rates:sta->supp_rates[local->hw.conf.channel->band] =
sdata->u.sta.supp_rates_bits[local->hw.conf.channel->band];because
sdata->u.sta.supp_rates_bitsis set only when we actually join an ibss, which is not the case in this scenario; so we assign zero here. Then, the code inrate_control_pid_rate_init()callsrate_lowest_index()for some reason, and since no supported rate is found, this warning is issued.
Quoted 4 lines
The question is how
sta->supp_ratesshould be initialized:- we could initialize it to our sta's rates, but then we could probably transmit to a station at unsupported rate
isn't this what is done right now, and the rateset is zero sometimes and then we get the warning?
this might be wrong anyways: as you said it could make us send frames at an unsupported rate.
Quoted 3 lines
- add new ibss station only on received beacon, not on a data frame; currently, beacons are ignored for this purpose (they just update the bss list later on)
i think stations should be added on reception of both beacons and data frames.
Quoted 1 line
- something else (like 1Mbps only)?
what about the rate of the currently received data frame (and maybe any other rates we could safely deduce from that)?
bruno
Quoted 9 lines
Quoted 6 lines
[...]
The question is how
sta->supp_ratesshould be initialized:- we could initialize it to our sta's rates, but then we could probably transmit to a station at unsupported rate
isn't this what is done right now, and the rateset is zero sometimes and then we get the warning?
Yes, kind-of. It is initialized to the rateset of an ibss we are part of, which is the one of ibss we are joining to, or our supported rateset if we create a new one. However, it is 0 before one of those 2 actions happen, and then we get the warning.
Quoted 2 lines
this might be wrong anyways: as you said it could make us send frames at an unsupported rate.
Actually, this can happen even now:
- we join an g-ibss, thus setting the rateset to 1-54
- we receive a data frame from a b-only station -> we assign all 1-54 rates to it
- we send something to this station
Probably not a big issue, as a) we will update the sta-rateset on its beacon, and b) I would expect that such an ibss would adapt to 1-11 only in the presence of b-only station..
Quoted 6 lines
Quoted 4 lines
- add new ibss station only on received beacon, not on a data frame; currently, beacons are ignored for this purpose (they just update the bss list later on)
i think stations should be added on reception of both beacons and data frames.
Or, do we need this information _before_ joining/creating a new ibss? Couldn't we just ignore all STAs around until we have a reason not to?
Quoted 5 lines
Quoted 2 lines
- something else (like 1Mbps only)?
what about the rate of the currently received data frame (and maybe any other rates we could safely deduce from that)?
Yes, that would be a reasonable option - providing that we have the rate (which we should - there is a WARN_ON(1) in rx-path if it is not set correctly)
As I think about that, I would suggest:
- no sta info is being collected prior to join/create
- sta entry is added/updated on each beacon with reported rateset
- sta entry is added/updated on data frames with just the received-rate
Vlado
Quoted 2 lines
bruno
Quoted 3 lines
Yes, that would be a reasonable option - providing that we have the rate (which we should - there is a
WARN_ON(1)in rx-path if it is not set correctly)
the packet is also dropped in that case so you don't see it.
Quoted 4 lines
As I think about that, I would suggest:
- no sta info is being collected prior to join/create
- sta entry is added/updated on each beacon with reported rateset
- sta entry is added/updated on data frames with just the received-rate
Want to do the patch?
johannes
Quoted 4 lines · Johannes Berg
Quoted 2 lines
Yes, that would be a reasonable option - providing that we have the rate (which we should - there is a
WARN_ON(1)in rx-path if it is not set correctly)the packet is also dropped in that case so you don't see it.
Oh yes. Should have read one more line of code :)
Quoted 7 lines
Quoted 5 lines
As I think about that, I would suggest:
- no sta info is being collected prior to join/create
- sta entry is added/updated on each beacon with reported rateset
- sta entry is added/updated on data frames with just the received-rateWant to do the patch?
I'll try. Hope we have rx-rate on hand where needed :)
Vlado
Quoted 19 lines
because
sdata->u.sta.supp_rates_bitsis set only when we actually join an ibss, which is not the case in this scenario; so we assign zero here. Then, the code inrate_control_pid_rate_init()callsrate_lowest_index()for some reason, and since no supported rate is found, this warning is issued.The question is how
sta->supp_ratesshould be initialized:- we could initialize it to our sta's rates, but then we could probably transmit to a station at unsupported rate
- add new ibss station only on received beacon, not on a data frame; currently, beacons are ignored for this purpose (they just update the bss list later on)
- something else (like 1Mbps only)?
Quoted 7 lines
As soon as we do
sta_join_ibss(), this warning won't happen again.Note that once we have sta entry (in our ibss), we will update its supported rates based on beacons it sends (in
rx_bss_info()).Any thoughts?
I don't know. I don't use IBSS nor am I intimately familiar with the specs for it.
johannes