Re: [PATCH v3] coresight: Fix scheduling while atomic in coresight_cpu_pm_notify()

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

On Fri, Jul 17, 2026 at 06:12:01PM +0200, Sebastian Andrzej Siewior wrote:

[...]

> > The raw spinlock (coresight_dev_lock) serializes access to the per-CPU
> > csdev_source pointer. It does not guarantee the lifetime of the source
> > or its _parent_ device. coresight_unregister() is not only reached from
> > module unload; it can also be called when a driver is unbind, for
> > example DT overlay removal or device hotplug/unplug.
> 
> But doesn't coresight_unregister() block on the coresight_dev_lock here?

Fair point.

coresight_cpu_get_active_path() can safely access the source while
holding coresight_dev_lock. Unregistration will be blocked until the
access from the CPU PM notifier has finished.

> > I think a proper fix needs a clearer lifetime model for an active
> > session. E.g., we could consider to call device_link_add() to prevent
> > device unbind / unregister, and unlink device when the session is
> > finished. Once that is in place, the CPU PM notifier can safely use the
> > active path without get_device()/put_device() pair anymore.
> 
> Right. I am also not sure about lifetime of coresight_device::path.

coresight_device::path is a runtime pointer that is valid only while
the device is enabled.

Since both the path and the device mode are updated atomically on the
local CPU, observing the device mode as enabled guarantees that the
corresponding coresight_device::path is valid.

Thanks,
Leo