Re: [PATCH v12 07/13] task_isolation: add debug boot flag

[Chris Metcalf]

(Oops, missed one that I should have forced to text/plain. Resending.)

On 5/18/2016 9:56 AM, Peter Zijlstra wrote:
> On Tue, Apr 05, 2016 at 01:38:36PM -0400, Chris Metcalf wrote:
> > +#ifdef CONFIG_TASK_ISOLATION
> > +void task_isolation_debug(int cpu)
> > +{
> > +	struct task_struct *p;
> > +
> > +	if (!task_isolation_possible(cpu))
> > +		return;
> > +
> > +	rcu_read_lock();
> > +	p = cpu_curr(cpu);
> > +	get_task_struct(p);
> > +	rcu_read_unlock();
> > +	task_isolation_debug_task(cpu, p);
> > +	put_task_struct(p);
> This is still broken...

I don't know how or why, though. :-)  Can you give me a better idiom?
This looks to my eye just like how it's done for something like
sched_setaffinity() by one task on another task, and I would have
assumed the risks there of the other task evaporating part way
through would be the same as the risks here.

> Also, I really don't like how you sprinkle a call all over the core
> kernel. At the very least make an inline fast path for this function to
> avoid the call whenever possible.

I can boost the "task_isolation_possible()" test up into a static inline,
and only call in the case where we have a target cpu that is actually
in the "task_isolation=" boot argument set.

--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com