Re: [PATCH v4 3/7] fs/resctrl: Add interface to disable a monitor event

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Tony,

On 3/30/26 2:43 PM, Tony Luck wrote:
> Architecture code can ask file system code to enable events. But there
> is no way to clean up and disable events.

Missing why it is required to disable events.

> 
> Add resctrl_disable_mon_event().

(can be seen from patch)

> Adding/removing events is only
> possible when the file system is not mounted. Add a WARN_ON() to

While this is accurate that it should not be possible to enable/disable
events while resctrl is mounted, this is *not* the *only* time when it
should not be possible. Here it is unfortunately not straight forward
since only some events require per-domain state which requires the event
to be enabled before any domain comes online, potentially very early in
initialization.

To me the addition of this warning adds false security.

Also, consider that resctrl_mounted is protected by rdtgroup_mutex and
this addition gives architecture code free access without any protection.

To do this right resctrl may need to add more state to an event but how
that may look is unclear since an architecture may require per-domain
architectural state for an event while resctrl fs needs none. At this
time these scenarios may just fall into the "architecture must do the
right thing" category since it has best information on how state is
managed for the events as they are enabled/disabled.

Reinette