Re: [PATCH v6 02/19] coresight: Set per-CPU source pointer

[Leo Yan <leo.yan@arm.com>]

On Fri, Mar 13, 2026 at 11:18:20AM +0000, Suzuki K Poulose wrote:

[...]

> >   static struct coresight_device *coresight_get_source(struct coresight_path *path)
> >   {
> >   	struct coresight_device *csdev;
> > @@ -1401,6 +1452,8 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> >   	mutex_unlock(&coresight_mutex);
> > +	coresight_set_percpu_source(csdev);
> > +
> >   	if (cti_assoc_ops && cti_assoc_ops->add)
> >   		cti_assoc_ops->add(csdev);
> > @@ -1427,6 +1480,7 @@ void coresight_unregister(struct coresight_device *csdev)
> >   	if (cti_assoc_ops && cti_assoc_ops->remove)
> >   		cti_assoc_ops->remove(csdev);
> > +	coresight_clear_percpu_source(csdev);
> 
> Should these be done with the mutex lock held ?

If so, we will create a locking chain:

  coresight_mutex -> cpus_read_lock()

Afterwards in patch 18, it uses cpus_read_lock() to protect sysfs knobs,
a reversed locking chain will be established:

  cpus_read_lock() -> coresight_mutex

LOCKDEP will complain for possible deadlock.  This is why this patch
avoids to acquire mutex when set / clear per CPU sources.

> >   	mutex_lock(&coresight_mutex);
> >   	etm_perf_del_symlink_sink(csdev);
> >   	coresight_remove_conns(csdev);
> > 
>