Re: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU

On Wed, Jul 11, 2018 at 02:53:22PM +0200, Peter Zijlstra wrote:

On Thu, Jun 28, 2018 at 11:21:46AM -0700, Joel Fernandes wrote:

...

• rcu_read_lock_sched_notrace();				\
  

• it_func_ptr = rcu_dereference_sched((tp)->funcs);	\
  

• 							\
  

• /*							\
  

•  * For rcuidle callers, use srcu since sched-rcu	\
  

•  * doesn't work from the idle path.			\
  

•  */							\
  

• if (rcuidle) {						\
  

• 	if (in_nmi()) {					\
  

• 		WARN_ON_ONCE(1);			\
  

• 		return; /* no srcu from nmi */		\
  

• 	}						\
  

• 							\
  

• 	idx = srcu_read_lock_notrace(&tracepoint_srcu);	\
  

• 	it_func_ptr =					\
  

• 		srcu_dereference_notrace((tp)->funcs,	\
  

• 				&tracepoint_srcu);	\
  

• 	/* To keep it consistent with !rcuidle path */	\
  

• 	preempt_disable_notrace();			\
  

• } else {						\
  

• 	rcu_read_lock_sched_notrace();			\
  

• 	it_func_ptr =					\
  

• 		rcu_dereference_sched((tp)->funcs);	\
  

• }							\
  

• 							\
  

  if (it_func_ptr) { \ do { \ it_func = (it_func_ptr)->func; \

@@ -148,9 +177,13 @@ extern void syscall_unregfunc(void); ((void(*)(proto))(it_func))(args); \ } while ((++it_func_ptr)->func); \ } \

• rcu_read_unlock_sched_notrace();			\
  

• if (rcucheck)						\
  

• 	rcu_irq_exit_irqson();				\
  

• 							\
  

• if (rcuidle) {						\
  

• 	preempt_enable_notrace();			\
  

• 	srcu_read_unlock_notrace(&tracepoint_srcu, idx);\
  

• } else {						\
  

• 	rcu_read_unlock_sched_notrace();		\
  

• }							\
  

  } while (0)

In fact, I would write the thing like:

preempt_disable_notrace();
if (rcuidle)
	idx = srcu_read_lock_notrace(&tracepoint_srcu);

it_func_ptr = rcu_dereference_raw((tp)->funcs);

/* ... */

if (rcu_idle)
	srcu_read_unlock_notrace(&tracepoint_srcu, idx);
preempt_enable_notrace();

Much simpler and very much the same.

Cool, thanks! I will do it this way and resend.

- Joel

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