Re: [PATCH v1 01/31] x86/resctrl: Fix allocation of cleanest CLOSID on platforms with no monitors

[Reinette Chatre]

Hi James,

On 3/21/2024 9:50 AM, James Morse wrote:
> commit 6eac36bb9eb0 ("x86/resctrl: Allocate the cleanest CLOSID by
> searching closid_num_dirty_rmid") added a Kconfig option that causes

Please see section about "Fixes" tags in section "Ordering of commit tags"
in Documentation/process/maintainer-tip.rst

> resctrl to search for the CLOSID with the fewest dirty cache lines when
> creating a new control group. This depends on the values read from the
> llc_occupancy counters.
> 
> This support missed that some platforms may not have these counters.
> This causes a NULL pointer dereference when creating a new control
> group as the array was not allocated by dom_data_init().
> 
> As this feature isn't necessary on platforms that don't have cache
> occupancy monitors, add this to the check that occurs when a new
> control group is allocated.
> 
> The existing code is not selected by any upstream platform, it makes
> no sense to backport this patch to stable.
> 
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 011e17efb1a6..1767c1affa60 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -149,7 +149,8 @@ static int closid_alloc(void)
>  
>  	lockdep_assert_held(&rdtgroup_mutex);
>  
> -	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID)) {
> +	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID) &&
> +	    is_llc_occupancy_enabled()) {
>  		cleanest_closid = resctrl_find_cleanest_closid();
>  		if (cleanest_closid < 0)
>  			return cleanest_closid;

Patch looks good.

Thank you

Reinette