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

[Dave Martin <Dave.Martin@arm.com>]

On Mon, Apr 08, 2024 at 08:13:40PM -0700, Reinette Chatre wrote:
> 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

Noted for James' attention.

> > 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@arm.com>
> > ---
> >  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
> 

Noted, thanks.

Cheers
---Dave