On Wed, Jul 31, 2013 at 11:09 AM, Felix Fietkau <nbd@xxxxxxxxxxx> wrote:
> On 2013-07-31 10:39 AM, Arend van Spriel wrote:
>> Hi Felix,
>>
>> How are things in OpenWRT. I wanted to ask you something regarding a
>> defect I am looking at. Since kernel 3.9 several reports have been made
>> about a kernel panic in brcmsmac, ie. a divide-by-zero error.
> 3.9 was the first kernel to support CCK rates in minstrel_ht as
> fallback (in case the link gets very bad). Not sure if that triggers
> anything weird in brcmsmac.
>
>> Debugging the issue shows we end up with a rate with MCS index 110,
>> which is, well, impossible.
> Did you verify that it comes directly from minstrel_ht, or does it show
> up somewhere further down the chain in brcmsmac?
>
>> As brcmsmac gets the rate info from
>> minstrel_ht I was wondering if we have an intergration issue here. I saw
>> around April patches about new API which may have been in the 3.9 time
>> frame and something subtly changed things for brcmsmac.
> The new rate API was added in 3.10, not 3.9. It did add bug that caused
> bogus MCS rates. I've sent a patch for this a while back (shortly
> before 3.10 was released), but it was too late to make it into the
> release. I guess we have to wait for it to be applied through stable -
> no idea why that hasn't happened yet.
>
> Here is the fix:
>
> commit 1cd158573951f737fbc878a35cb5eb47bf9af3d5
> Author: Felix Fietkau <nbd@xxxxxxxxxxx>
> Date: Fri Jun 28 21:04:35 2013 +0200
>
> mac80211/minstrel_ht: fix cck rate sampling
>
That patch is not in Linus tree yet, so it won't get into stable.
- Sedat -
> The CCK group needs special treatment to set the right flags and rate
> index. Add this missing check to prevent setting broken rates for tx
> packets.
>
> Cc: stable@xxxxxxxxxxxxxxx # 3.10
> Signed-off-by: Felix Fietkau <nbd@xxxxxxxxxxx>
> Signed-off-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
>
> diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
> index 5b2d301..f5aed96 100644
> --- a/net/mac80211/rc80211_minstrel_ht.c
> +++ b/net/mac80211/rc80211_minstrel_ht.c
> @@ -804,10 +804,18 @@ minstrel_ht_get_rate(void *priv, struct ieee80211_sta *sta, void *priv_sta,
>
> sample_group = &minstrel_mcs_groups[sample_idx / MCS_GROUP_RATES];
> info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
> + rate->count = 1;
> +
> + if (sample_idx / MCS_GROUP_RATES == MINSTREL_CCK_GROUP) {
> + int idx = sample_idx % ARRAY_SIZE(mp->cck_rates);
> + rate->idx = mp->cck_rates[idx];
> + rate->flags = 0;
> + return;
> + }
> +
> rate->idx = sample_idx % MCS_GROUP_RATES +
> (sample_group->streams - 1) * MCS_GROUP_RATES;
> rate->flags = IEEE80211_TX_RC_MCS | sample_group->flags;
> - rate->count = 1;
> }
>
> static void
>
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