Re: RCU question

[Dipankar Sarma <dipankar@in.ibm.com>]

On Thu, Dec 09, 2004 at 03:59:45PM -0800, George Anzinger wrote:
> I am working on VST code.  This code is called from the idle loop to check 
> for future timers.  It then sets up a timer to interrupt in time to handle 
> the nearest timer and turns off the time base interrupt source.  As part of 
> qualifying the entry to this state I want to make sure there is no pending 
> work so, from the idle task I have this:
> 
> 	if (local_softirq_pending())
> 		do_softirq();
> 
> 	BUG_ON(local_softirq_pending());
> 
> I did not really expect to find any pending softirqs, but, not only are 
> there some, they don't go away and the system BUGs.  The offender is the 
> RCU task. The question is: is this normal or is there something wrong?

Why do you think there would not be any softirq pending after do_softirq() ?
What if the cpu gets a network interrupt which raises a softirq ?
And yes, RCU processing in softirq context can re-raise the softirq.
AFAICS, it is perfectly normal.

Thanks
Dipankar