Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing update_rq_clock()

[Peter Zijlstra]

On Wed, Sep 21, 2016 at 05:58:27PM +0200, Petr Mladek wrote:
> > +static inline void assert_clock_updated(struct rq *rq)
> > +{
> > +#ifdef CONFIG_SCHED_DEBUG
> > +	/*
> > +	 * The only reason for not seeing a clock update since the
> > +	 * last rq_pin_lock() is if we're currently skipping updates.
> > +	 */
> > +	WARN_ON_ONCE(rq->clock_update_flags < RQCF_ACT_SKIP);
> > +#endif
> > +}
> 
> I am afraid that it might eventually create a deadlock.
> For example, there is the following call chain:
> 

Yeah, meh. There's already plenty WARNs in the sched code. The idea of
course being that they should not trigger. If they do, something
buggered already, so who bloody cares about a deadlock later ;-)