Re: [PATCH v12 06/25] arm,x86,fs/resctrl: Replace architecture resctrl_arch_{alloc,mon}_capable()

[Luck, Tony]

Hi Reinette,

On Thu, Sep 24, 2026 at 08:22:47AM -0700, Reinette Chatre wrote:
> Hi Tony,
> 
> On 9/16/26 4:13 PM, Tony Luck wrote:
> > All the information to determine whether a system is alloc, or mon,
> > capable is available to the file system. Architecture helpers are not
> 
> nit: "is alloc, or mon, capable" -> "is capable of allocation or monitoring"?
> 
> > needed.
> > 
> > Define generic resctrl_alloc_capable() and resctrl_mon_capable() and
> > replace all architecture versions.
> > 
> > Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> > Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> > ---
> 
> Please note that the pending RISC-V enabling [1] is not compatible with this
> change but there is a change planned that will let resctrl_alloc_capable()
> introduced here work on RISC-V also. We need to coordinate these two
> series.

The first few patches in this series have relatively simple cleanups
suggested. Perhaps when I post v13 you could focus on getting these to
the finish line and have Boris consider them for inclusion.

That would get this change into TIP x86/cache and let the RISC-V
folks move forward.

Note there will be one new patch in the initial sequence. The bug
fix for is_closid_match() that you suggested I separate out from
patch 9.

Draft version of new patch below.

> 
> | Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> 
> Reinette
> 
> [1] https://lore.kernel.org/lkml/20260917-dfustini-atl-sc-cbqri-dt-v8-2-7964e8d73fe8@xxxxxxxxxx/

-Tony

commit 986bf1a4e789de917e955fe549bdd71e51dc2e48
Author: Tony Luck <tony.luck@xxxxxxxxx>
Date:   Thu Sep 24 12:40:41 2026 -0700

    fs/resctrl: Ensure default group reports tasks on monitor-only systems
    
    Sashiko reported[1]:
    
      This is a pre-existing issue, but the resctrl_alloc_capable() check in
      is_closid_match() actively breaks the default group on systems that only
      support monitoring capabilities.
      When a user reads the root /sys/fs/resctrl/tasks file on a system with
      monitoring capabilities but no allocation capabilities, the following call
      chain occurs:
      rdtgroup_tasks_show()
        show_rdt_tasks()
          is_closid_match()
      Since resctrl_alloc_capable() evaluates to false on such systems,
      is_closid_match() unconditionally returns false for all tasks. Furthermore,
      because the default group has type RDTCTRL_GROUP, is_rmid_match() will also
      return false.
      This causes the root tasks file to appear completely empty, hiding all tasks
      on the system that have not been explicitly moved to a monitoring group.
    
    Remove the resctrl_alloc_capable() check from is_closid_match().
    
    Fixes: e6b2fac36fcc ("x86/resctrl: Use is_closid_match() in more places")
    Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
    Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
    Link: https://sashiko.dev/#/patchset/20260831174421.13921-1-tony.luck%40intel.com?part=9 # [1]
    ---
    v13:
            New patch (split from patch 9)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 5dcbb0a964e8..6733ed174f51 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -685,7 +685,7 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 
 static bool is_closid_match(struct task_struct *t, struct rdtgroup *r)
 {
-	return (resctrl_arch_alloc_capable() && (r->type == RDTCTRL_GROUP) &&
+	return (r->type == RDTCTRL_GROUP &&
 		resctrl_arch_match_closid(t, r->closid));
 }