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

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