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SubjectRe: [RFC PATCH V2 2/7] perf: Init/fini PMU specific data
On Mon, Jan 06, 2020 at 06:23:43AM -0800, Andi Kleen wrote:
> > > + 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?

Or insize that raw_spin_lock. And last time I expressly said to not do
what whole tasklist iteration under a spinlock.

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