On Jan 28, 2008 11:07 AM, Larry Finger <Larry.Finger@xxxxxxxxxxxx> wrote:
> Johannes,
>
> With the latest wireless-2.6 git tree on my x86_64 system, I am getting a GPF in
> ieee80211_sta_scan_work. I tracked it down to the following astatement:
>
> if (!sband ||
> (local->scan_channel_idx >= sband->n_channels &&
> local->scan_band >= IEEE80211_NUM_BANDS)) {
>
> Specifically, it is the "local->scan_channel_idx >= sband->n_channels" part of the if test. When I
> added test prints of local->scan_channel_idx, local->scan_band, and sband, I got the following:
>
> mac80211: scan_channel_idx = 0, scan_band = 0, sband = ffffffff882c2f10
> mac80211: scan_channel_idx = 1, scan_band = 0, sband = ffffffff882c2f10
> ...
> ...
> mac80211: scan_channel_idx = 13, scan_band = 0, sband = ffffffff882c2f10
> mac80211: scan_channel_idx = 0, scan_band = 2, sband = dead4ead00000001
> general protection fault: 0000 [1] SMP
>
> As can be seen, "sband" is some kind of magic number and is an invalid pointer when scan_band is
> larger than IEEE80211_NUM_BANDS, which causes the GPF.
>
> With the following patch, it works:
>
> Index: wireless-2.6/net/mac80211/ieee80211_sta.c
> ===================================================================
> --- wireless-2.6.orig/net/mac80211/ieee80211_sta.c
> +++ wireless-2.6/net/mac80211/ieee80211_sta.c
> @@ -3237,8 +3237,7 @@ void ieee80211_sta_scan_work(struct work
> }
>
> if (!sband ||
> - (local->scan_channel_idx >= sband->n_channels &&
> - local->scan_band >= IEEE80211_NUM_BANDS)) {
> + local->scan_band >= IEEE80211_NUM_BANDS) {
> ieee80211_scan_completed(local_to_hw(local));
> return;
> }
>
> It seems to me that it should be OK to skip the scan_chan_idx >= sband->n_channels part of the test
> as scan_band won't get to be >= to IEEE80211_NUM_BANDS until all the channels have been tested in
> the legal bands.
>
> Larry
There are too many issues with API change patch. I think it is a good
direction but it's really unstable I think we need to give another
round before it can be applied.
Thanks
Tomas
>
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