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SubjectRe: [RFC PATCH V2 2/7] perf: Init/fini PMU specific data
> > +	rcu_read_lock();
> > + for_each_process_thread(g, p) {
> > + mutex_lock(&p->perf_event_mutex);
> > + if (p->perf_ctx_data) {
> > + /*
> > + * The perf_ctx_data for this thread may has been
> > + * allocated by per-task event.
> > + * Only update refcount for the case.
> > + */
> > + refcount_inc(&p->perf_ctx_data->refcount);
> > + mutex_unlock(&p->perf_event_mutex);
> > + continue;
> > + }
> > +
> > + if (pos < num_thread) {
> > + refcount_set(&data[pos]->refcount, 1);
> > + rcu_assign_pointer(p->perf_ctx_data, data[pos++]);
> > + } else {
> > + /*
> > + * There may be some new threads created,
> > + * when we allocate space.
> > + * Track the number in nr_new_tasks.
> > + */
> > + nr_new_tasks++;
> > + }
> > + mutex_unlock(&p->perf_event_mutex);
> > + }
> > + rcu_read_unlock();
> > +
> > + raw_spin_unlock_irqrestore(&task_data_sys_wide_events_lock, flags);
>
> Still NAK. That's some mightly broken code there.

Yes, Kan you cannot use a mutex (sleeping) inside rcu_read_lock().
Can perf_event_mutex be a spin lock?

-Andi

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