New subject: [tip: x86/urgent] x86/resctrl: Don't move a task to the same resource group

17 Dec 2020

From: Fenghua Yu fenghua.yu@intel.com
Shakeel Butt reported in [1] that a user can request a task to be moved
to a resource group even if the task is already in the group. It just
wastes time to do the move operation which could be costly to send IPI
to a different CPU.
Add a sanity check to ensure that the move operation only happens when
the task is not already in the resource group.
[1] https://lore.kernel.org/lkml/CALvZod7E9zzHwenzf7objzGKsdBmVwTgEJ0nPgs0LUFU3S...
Fixes: e02737d5b826 ("x86/intel_rdt: Add tasks files")
Reported-by: Shakeel Butt shakeelb@google.com
Signed-off-by: Fenghua Yu fenghua.yu@intel.com
Signed-off-by: Reinette Chatre reinette.chatre@intel.com
Reviewed-by: Tony Luck tony.luck@intel.com
Cc: stable@vger.kernel.org
---
V1->V2:
* No changes
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index c5937a12d731..4042e1eb4f5d 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -552,6 +552,13 @@ static void update_task_closid_rmid(struct task_struct *t)
 static int __rdtgroup_move_task(struct task_struct *tsk,
    			struct rdtgroup *rdtgrp)
 {
+	/* If the task is already in rdtgrp, no need to move the task. */
+	if ((rdtgrp->type == RDTCTRL_GROUP && tsk->closid == rdtgrp->closid &&
+	     tsk->rmid == rdtgrp->mon.rmid) ||
+	    (rdtgrp->type == RDTMON_GROUP && tsk->rmid == rdtgrp->mon.rmid &&
+	     tsk->closid == rdtgrp->mon.parent->closid))
+		return 0;
+
    /*
     * Set the task's closid/rmid before the PQR_ASSOC MSR can be
     * updated by them.
-- 
2.26.2


    

[PATCH V2 2/4] x86/resctrl: Don't move a task to the same resource group