Re: [PATCH v3 31/38] x86/resctrl: resctrl_exit() teardown resctrl but leave the mount point

[Reinette Chatre]

Hi James,

On 6/14/24 8:00 AM, James Morse wrote:
> resctrl_exit() was intended for use when the 'resctrl' module was unloaded.
> resctrl can't be built as a module, and the kernfs helpers are not exported
> so this is unlikely to change. MPAM has an error interrupt which indicates
> the MPAM driver has gone haywire. Should this occur tasks could run with
> the wrong control values, leading to bad performance for impoartant tasks.

impoartant -> important

> The MPAM driver needs a way to tell resctrl that no further configuration
> should be attempted.
>
> Using resctrl_exit() for this leaves the system in a funny state as
> resctrl is still mounted, but cannot be un-mounted because the sysfs
> directory that is typically used has been removed. Dave Martin suggests
> this may cause systemd trouble in the future as not all filesystems
> can be unmounted.
>
> Add calls to remove all the files and directories in resctrl, and
> remove the sysfs_remove_mount_point() call that leaves the system
> in a funny state. When triggered, this causes all the resctrl files
> to disappear. resctrl can be unmounted, but not mounted again.

I am not familiar with these flows so I would like to confirm ...
In this scenario the resctrl filesystem will be unregistered, are
you saying that it is possible to unmount a filesystem after it has
been unregistered?

Reinette