Re: What are the general causes of frozen system?

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Sat, 2005-11-26 at 20:44 -0600, Larry Finger wrote:
> I am trying to help the bcm43xx project develop a driver for the 
> Broadcom 43xx wireless chips, using my Linksys WPC54G card. 
> Unfortunately, since the group got far enough to turn on RX DMA, my 
> system has frozen whenever I load the driver. TX DMA was OK. It seems to 
> correlate with the receipt of a beacon from my AP, but that cannot be 
> proven. When the freeze happens, I cannot do anything more and have to 
> power the system off.
> 
> What should I consider as a cause of the freeze? I have reviewed the 
> code and do not find any obvious out-of-bounds memory references. I have 
> tried various 'printk' statements, but none of them in the bottom-half 
> interrupt routine make it to the logs. Are there any tricks that I 
> should try?

spinlock debugging is one... if it's a bad DMA to low memory, you can't
do much. Another common cause is a stale interrupt, is your IRQ handler
called over & over again in a loop ?

The problem is that depending on what you are interrupting, printk may
not work ...

Ben.