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

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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 ;-)

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[PATCH v2 0/7] sched: Diagnostic checks for missing rq clock updates Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:40 +0200
  [PATCH v2 5/7] sched/core: Reset RQCF_ACT_SKIP before unpinning rq->lock Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:40 +0200
  [PATCH v2 3/7] sched/fair: Update rq clock in task_hot() Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:40 +0200
  [PATCH v2 2/7] sched/fair: Update rq clock before waking up new task Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:40 +0200
  [PATCH v2 7/7] sched/core: Add debug code to catch missing update_rq_clock() Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:40 +0200
    Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Petr Mladek <pmladek@suse.com> - 2016-09-21 18:00 +0200
      Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 21:10 +0200
        Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Thomas Gleixner <tglx@linutronix.de> - 2016-09-21 21:50 +0200
        Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-09-22 02:50 +0200
      Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Peter Zijlstra <peterz@infradead.org> - 2016-09-22 10:10 +0200
        Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Jan Kara <jack@suse.cz> - 2016-09-22 10:40 +0200
          Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Peter Zijlstra <peterz@infradead.org> - 2016-09-22 11:40 +0200
            Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing  update_rq_clock() Peter Zijlstra <peterz@infradead.org> - 2016-09-22 13:30 +0200
  [PATCH v2 4/7] sched: Add wrappers for lockdep_(un)pin_lock() Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:40 +0200
  [PATCH v2 6/7] sched/fair: Push rq lock pin/unpin into idle_balance() Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:40 +0200
  [PATCH v2 1/7] sched/fair: Update the rq clock before detaching tasks Matt Fleming <matt@codeblueprint.co.uk> - 2016-09-21 15:50 +0200

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