Hello.

I'd like to apologize in advance, if I shouldn't report such issues to 
this mailing list. I was told this is a good place for bug reports 
associated with Linux kernel modules for wireless devices.

I have a ThinkPad X201 Tablet, which I recently bought used. This laptop 
has an Intel Centrino Ultimate-N 6300 wireless 802.11abgn card, which is 
supported via the iwlwifi module and a firmware image. I'm using Arch 
Linux on it (i haven't tried a different OS yet), and so have fairly 
recent and vanilla kernel and firmware packages (the policy of this 
distribution is to have the latest packages marked as stable by upstream 
and only do patching if it's required to build the package or make it 
work with others).

Since some time I've been struggling with my laptop's wifi card randomly 
locking up (at least, I think the hardware locks up), usually after at 
least a few hours of usage. The initial symptom of such an event is the 
wifi card ceasing to work. Afterwards, each few seconds the computer 
"freezes" for a few other seconds. I can stop these freezes by flipping 
a radio disable switch, which causes rfkill's hard block on all wireless 
devices. However, flipping it back to unblock doesn't cause the wifi 
card to function, only bringing back aforementioned freezes.

These lock-ups happen completely randomly. I'm using this laptop a lot, 
over 10 hours daily, and there are days when there is no problem. I even 
managed to use it a week without problems. Other times it can happen as 
much as 4 times daily. Twice it happened straight after boot, but 
otherwise it happens after at least a few hours of usage.

I at first thought, that it might be associated with the amount of data 
sent in and out of the interface, but there was no correlation. I 
specially tested this by moving large amounts of data within my local 
network for a few hours. Next thing I considered, was that the device 
overheats due to radiation (I'm usually very close to my AP, and have 
the default tx-power setting, which is 15dBm). But these issues happened 
no matter how far I was and changing tx-power to smallest possible value 
didn't help. I also thought this might be because the device accumulates 
heat after a few hours, but recently I got the lock-up 3 minutes after 
boot, which happened after the laptop was laying all night powered off.

Since this issues started, I've considered many packages (such as those 
network-related and kernel modules like tp-smapi) as the culprits 
(especially those installed or updated around the time of the first 
occurrence) and tried uninstalling or downgrading. I also tried removing 
any module options and udev rules I made before the lock-ups started. 
Again, no success.

Finally, I recently tried a few options of the iwlwifi module 
(11n_disable=1, swcrypto=1, bt_coex_active=0). None of those helped, 
though after setting bt_coex_active=0 I had 2 days of peace. I haven't 
tried the power-saving ones yet, though.

My only remaining clue is that this seems more likely to happen if I'm 
on battery power, especially when the battery has little charge. So I 
guess this might be associated with power management.

I have to say, I don't have the knowledge to understand what's really 
going on, how to read the ring buffer output or how to debug such an 
issue. But it seems to me, looking at the dmesg output, that the driver 
has some issue, the device is reinitialized, which fails. Hence why I 
wrote that the device locks up.

I've attached output of dmesg captured right after a recent lock-up. I 
hope I have a recent enough kernel for this to be useful. I also 
attached outputs of dmidecode and lspci -vvvv, and /proc/config.gz, in 
case this information would be useful.

Please tell me if anything else is needed. I'm willing to invest some 
time and have no problem with things like compiling a custom kernel, 
using gdb. The only problem here is that I have no idea how I can 
trigger this, and can never be sure if the issue went away.

I thank in advance for any help.

Sincerely,
Jeremy.