linux-kernel - Re: [PATCH -rcu dev 1/3] rcu/tree: tick_dep_set/clear

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Date:   Mon, 19 Aug 2019 18:32:27 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: [PATCH -rcu dev 1/3] rcu/tree: tick_dep_set/clear_cpu should
 accept bits instead of masks

On Mon, Aug 19, 2019 at 07:46:32AM -0700, Paul E. McKenney wrote:
> On Mon, Aug 19, 2019 at 02:38:38PM +0200, Frederic Weisbecker wrote:
> > On Thu, Aug 15, 2019 at 10:53:09PM -0400, Joel Fernandes (Google) wrote:
> > > This commit fixes the issue.
> > > 
> > > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > > ---
> > >  kernel/rcu/tree.c | 29 +++++++++++++++++------------
> > >  1 file changed, 17 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 0512de9ead20..322b1b57967c 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -829,7 +829,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
> > >  		   !rdp->dynticks_nmi_nesting &&
> > >  		   rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
> > >  		rdp->rcu_forced_tick = true;
> > > -		tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU);
> > > +		tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
> > 
> > Did I suggest you to use the _MASK_ value? That was a bit mean.
> > Sorry for all that lost debugging time :-(
> 
> At some point, I should have looked at the other calls to these
> functions.  :-/
> 
> But would the following patch make sense?  This would not help for (say)
> use of TICK_MASK_BIT_POSIX_TIMER instead of TICK_DEP_BIT_POSIX_TIMER, but
> would help for any new values that might be added later on.  And currently
> for TICK_DEP_MASK_CLOCK_UNSTABLE and TICK_DEP_MASK_RCU.

I'd rather make the TICK_DEP_MASK_* values private to kernel/time/tick-sched.c but
that means I need to re-arrange a bit include/trace/events/timer.h

I'm looking into it. Meanwhile, your below patch that checks for the max value is
still valuable.

Thanks.

> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index 39eb44564058..4ed788ce5762 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -111,6 +111,7 @@ enum tick_dep_bits {
>  	TICK_DEP_BIT_CLOCK_UNSTABLE	= 3,
>  	TICK_DEP_BIT_RCU		= 4
>  };
> +#define TICK_DEP_BIT_MAX TICK_DEP_BIT_RCU
>  
>  #define TICK_DEP_MASK_NONE		0
>  #define TICK_DEP_MASK_POSIX_TIMER	(1 << TICK_DEP_BIT_POSIX_TIMER)
> @@ -215,24 +216,28 @@ extern void tick_nohz_dep_clear_signal(struct signal_struct *signal,
>   */
>  static inline void tick_dep_set(enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_set(bit);
>  }
>  
>  static inline void tick_dep_clear(enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_clear(bit);
>  }
>  
>  static inline void tick_dep_set_cpu(int cpu, enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_cpu(cpu))
>  		tick_nohz_dep_set_cpu(cpu, bit);
>  }
>  
>  static inline void tick_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_cpu(cpu))
>  		tick_nohz_dep_clear_cpu(cpu, bit);
>  }
> @@ -240,24 +245,28 @@ static inline void tick_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
>  static inline void tick_dep_set_task(struct task_struct *tsk,
>  				     enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_set_task(tsk, bit);
>  }
>  static inline void tick_dep_clear_task(struct task_struct *tsk,
>  				       enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_clear_task(tsk, bit);
>  }
>  static inline void tick_dep_set_signal(struct signal_struct *signal,
>  				       enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_set_signal(signal, bit);
>  }
>  static inline void tick_dep_clear_signal(struct signal_struct *signal,
>  					 enum tick_dep_bits bit)
>  {
> +	WARN_ON_ONCE(bit > TICK_DEP_BIT_MAX);
>  	if (tick_nohz_full_enabled())
>  		tick_nohz_dep_clear_signal(signal, bit);
>  }