Re: [PATCH v10 08/30] x86/resctrl: resctrl_exit() teardown resctrl but leave the mount point

[Reinette Chatre]

Hi James,

On 5/8/25 10:18 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 important tasks.
> In this scenario the MPAM driver will reset the hardware, but it needs
> a way to tell resctrl that no further configuration should be attempted.
> 
> In particular, moving tasks between control or monitor groups does not
> interact with the architecture code, so there is no opportunity for the
> arch code to indicate that the hardware is no-longer functioning.
> 
> 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.
> 
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Tested-by: Carl Worth <carl@xxxxxxxxxxxxxxxxxxxxxx> # arm64
> Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
> Tested-by: Peter Newman <peternewman@xxxxxxxxxx>
> Tested-by: Amit Singh Tomar <amitsinght@xxxxxxxxxxx> # arm64
> Tested-by: Shanker Donthineni <sdonthineni@xxxxxxxxxx> # arm64
> Tested-by: Babu Moger <babu.moger@xxxxxxx>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---

Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>

Reinette