linux-kernel - Re: [PATCH v2 11/11] lockdep,trace: Expose tracepoints

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Message-ID: <20200903155402.GO29330@paulmck-ThinkPad-P72>
Date:   Thu, 3 Sep 2020 08:54:02 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     peterz@...radead.org
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
        mingo@...nel.org, will@...nel.org, npiggin@...il.com,
        elver@...gle.com, jgross@...e.com, rostedt@...dmis.org,
        rjw@...ysocki.net, joel@...lfernandes.org, svens@...ux.ibm.com,
        tglx@...utronix.de, ulf.hansson@...aro.org,
        viresh.kumar@...aro.org, vincent.guittot@...aro.org
Subject: Re: [PATCH v2 11/11] lockdep,trace: Expose tracepoints

On Thu, Sep 03, 2020 at 05:36:49PM +0200, peterz@...radead.org wrote:
> On Thu, Sep 03, 2020 at 08:19:38AM -0700, Guenter Roeck wrote:
> > This doesn't compile for me - there is no "name" parameter in __DO_TRACE().
> > 
> > Error log:
> > In file included from ./include/linux/rculist.h:11,
> >                  from ./include/linux/pid.h:5,
> >                  from ./include/linux/sched.h:14,
> >                  from ./include/linux/sched/numa_balancing.h:10,
> >                  from ./include/trace/events/sched.h:8,
> >                  from kernel/sched/core.c:10:
> > ./include/trace/events/sched.h: In function 'trace_sched_kthread_stop':
> > ./include/linux/tracepoint.h:175:26: error: '__tracepoint_name' undeclared
> > 
> > I applied your patch on top of v5.9-rc3-75-gfc3abb53250a. Are you using
> > a different branch ?
> 
> Argh, I was on tip/master... easy fix though.
> 
> ---
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 7d9c1c0e149c..878bac893e41 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -27,17 +27,20 @@
>   *         SOFTIRQ_MASK:	0x0000ff00
>   *         HARDIRQ_MASK:	0x000f0000
>   *             NMI_MASK:	0x00f00000
> + *         RCUIDLE_MASK:	0x01000000
>   * PREEMPT_NEED_RESCHED:	0x80000000
>   */
>  #define PREEMPT_BITS	8
>  #define SOFTIRQ_BITS	8
>  #define HARDIRQ_BITS	4
>  #define NMI_BITS	4
> +#define RCUIDLE_BITS	1
>  
>  #define PREEMPT_SHIFT	0
>  #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
>  #define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
>  #define NMI_SHIFT	(HARDIRQ_SHIFT + HARDIRQ_BITS)
> +#define RCUIDLE_SHIFT	(NMI_SHIFT     + NMI_BITS)
>  
>  #define __IRQ_MASK(x)	((1UL << (x))-1)
>  
> @@ -45,11 +48,13 @@
>  #define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
>  #define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
>  #define NMI_MASK	(__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)
> +#define RCUIDLE_MASK	(__IRQ_MASK(RCUIDLE_BITS) << RCUIDLE_SHIFT)
>  
>  #define PREEMPT_OFFSET	(1UL << PREEMPT_SHIFT)
>  #define SOFTIRQ_OFFSET	(1UL << SOFTIRQ_SHIFT)
>  #define HARDIRQ_OFFSET	(1UL << HARDIRQ_SHIFT)
>  #define NMI_OFFSET	(1UL << NMI_SHIFT)
> +#define RCUIDLE_OFFSET	(1UL << RCUIDLE_SHIFT)
>  
>  #define SOFTIRQ_DISABLE_OFFSET	(2 * SOFTIRQ_OFFSET)
>  
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 598fec9f9dbf..0469bc1c24fc 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -164,12 +164,18 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  		void *__data;						\
>  		int __maybe_unused __idx = 0;				\
>  									\
> -		if (!(cond))						\
> +		if (!(cond) || (preempt_count() & RCUIDLE_MASK))	\
>  			return;						\
>  									\
>  		/* srcu can't be used from NMI */			\
>  		WARN_ON_ONCE(rcuidle && in_nmi());			\
>  									\
> +		if (IS_ENABLED(CONFIG_LOCKDEP) && !(rcuidle)) {		\
> +			rcu_read_lock_sched_notrace();			\
> +			rcu_dereference_sched((tp)->funcs);		\
> +			rcu_read_unlock_sched_notrace();		\
> +		}							\
> +									\
>  		/* keep srcu and sched-rcu usage consistent */		\
>  		preempt_disable_notrace();				\
>  									\
> @@ -235,11 +241,6 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  				TP_PROTO(data_proto),			\
>  				TP_ARGS(data_args),			\
>  				TP_CONDITION(cond), 0);			\
> -		if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) {		\
> -			rcu_read_lock_sched_notrace();			\
> -			rcu_dereference_sched(__tracepoint_##name.funcs);\
> -			rcu_read_unlock_sched_notrace();		\
> -		}							\
>  	}								\
>  	__DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args),		\
>  		PARAMS(cond), PARAMS(data_proto), PARAMS(data_args))	\
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 8ce77d9ac716..ad9fb4f12c63 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -269,6 +269,8 @@ static noinstr void rcu_dynticks_eqs_enter(void)
>  	/* Better not have special action (TLB flush) pending! */
>  	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
>  		     (seq & RCU_DYNTICK_CTRL_MASK));
> +
> +	__preempt_count_add(RCUIDLE_OFFSET);

But the rcu_data structure's ->dynticks field is still to be used in cases
where the RCU grace-period kthread must do off-CPU access to the CPU's
RCU-idle state, correct?  (Otherwise, some memory barriers are needed.)

							Thanx, Paul

>  }
>  
>  /*
> @@ -281,6 +283,8 @@ static noinstr void rcu_dynticks_eqs_exit(void)
>  	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>  	int seq;
>  
> +	__preempt_count_sub(RCUIDLE_OFFSET);
> +
>  	/*
>  	 * CPUs seeing atomic_add_return() must see prior idle sojourns,
>  	 * and we also must force ordering with the next RCU read-side
> 
>