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SubjectRe: [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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