iwlwifi bug when extending a channel struct

I ran into an issue with iwlagn when working on some patches for cfg80211. Initially I thought it was my own patches (even though they didn't touch iwlagn) due to some horrible memory corruption issue. As it turns out it was my patches but I can reproduce this with this simple patch below.

index d815aa8..64a1925 100644
@@ -82,6 +82,7 @@ struct ieee80211_channel {
 	int max_power;
 	u32 orig_flags;
 	int orig_mag, orig_mpwr;
+	bool bug;
 };
 
 /**

What ends up happening is the wiphy's band channels get all mangled up:

Frequencies:
* 2412 MHz [1] (14.0 dBm)
* 2 MHz [-481] (disabled)
* 32 MHz [-475] (0.0 dBm) (passive scanning, no IBSS, radar detection)
* 255 MHz [-430] (0.0 dBm)
* 14 MHz [-478] (0.0 dBm)
* 0 MHz [-481] (2442.0 dBm)
* 0 MHz [-481] (8.0 dBm)
* 0 MHz [-481] (16.0 dBm) (no IBSS)
* 0 MHz [-481] (255.0 dBm) (passive scanning, radar detection)
* 2462 MHz [11] (14.0 dBm)
* 0 MHz [-481] (0.0 dBm)

Frequencies:
* 5180 MHz [36] (15.0 dBm) (passive scanning, no IBSS)
* 40 MHz [-473] (disabled)
* 38 MHz [-473] (disabled)
* 255 MHz [-430] (0.0 dBm) (passive scanning, no IBSS)
* 15 MHz [-478] (0.0 dBm)
* 30 MHz [-475] (5300.0 dBm)
* 0 MHz [-481] (64.0 dBm)
* 0 MHz [-481] (disabled)
* 0 MHz [-481] (disabled)
* 5785 MHz [157] (16.0 dBm) (passive scanning, no IBSS)
* 161 MHz [-449] (disabled)
* 54 MHz [-470] (0.0 dBm)
* 0 MHz [-481] (0.0 dBm)

If I revert this patch I get what I would expect:

Frequencies:
* 2412 MHz [1] (14.0 dBm)
* 2417 MHz [2] (14.0 dBm)
* 2422 MHz [3] (14.0 dBm)
* 2427 MHz [4] (14.0 dBm)
* 2432 MHz [5] (14.0 dBm)
* 2437 MHz [6] (14.0 dBm)
* 2442 MHz [7] (14.0 dBm)
* 2447 MHz [8] (14.0 dBm)
* 2452 MHz [9] (14.0 dBm)
* 2457 MHz [10] (14.0 dBm)
* 2462 MHz [11] (14.0 dBm)

Frequencies:
* 5180 MHz [36] (15.0 dBm) (passive scanning, no IBSS)
* 5200 MHz [40] (15.0 dBm) (passive scanning, no IBSS)
* 5220 MHz [44] (15.0 dBm) (passive scanning, no IBSS)
* 5240 MHz [48] (15.0 dBm) (passive scanning, no IBSS)
* 5260 MHz [52] (15.0 dBm) (passive scanning, no IBSS, radar detection)
* 5280 MHz [56] (15.0 dBm) (passive scanning, no IBSS, radar detection)
* 5300 MHz [60] (15.0 dBm) (passive scanning, no IBSS, radar detection)
* 5320 MHz [64] (15.0 dBm) (passive scanning, no IBSS, radar detection)
* 5745 MHz [149] (16.0 dBm) (passive scanning, no IBSS)
* 5765 MHz [153] (16.0 dBm) (passive scanning, no IBSS)
* 5785 MHz [157] (16.0 dBm) (passive scanning, no IBSS)
* 5805 MHz [161] (16.0 dBm) (passive scanning, no IBSS)
* 5825 MHz [165] (16.0 dBm) (passive scanning, no IBSS)

I have a patch in my queue which adds a new element to ieee80211_channel but unfortunately it cannot get merged until this is fixed. I tried to look into it but I didn't see anything immediately obvious.

Luis

So after a fresh kernel install and reboot I do not see this issue any more, so who knows WTF was going on.

Luis