x86/intel_rdt/cqm: Add tasks file support

The root directory, ctrl_mon and monitor groups are populated
with a read/write file named "tasks". When read, it shows all the task
IDs assigned to the resource group.

Tasks can be added to groups by writing the PID to the file. A task can
be present in one "ctrl_mon" group "and" one "monitor" group. IOW a
PID_x can be seen in a ctrl_mon group and a monitor group at the same
time. When a task is added to a ctrl_mon group, it is automatically
removed from the previous ctrl_mon group where it belonged. Similarly if
a task is moved to a monitor group it is removed from the previous
monitor group . Also since the monitor groups can only have subset of
tasks of parent ctrl_mon group, a task can be moved to a monitor group
only if its already present in the parent ctrl_mon group.

Task membership is indicated by a new field in the task_struct "u32
rmid" which holds the RMID for the task. RMID=0 is reserved for the
default root group where the tasks belong to at mount.

[tony: zero the rmid if rdtgroup was deleted when task was being moved]
Signed-off-by: Tony Luck <tony.luck@linux.intel.com>
Signed-off-by: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: ravi.v.shankar@intel.com
Cc: tony.luck@intel.com
Cc: fenghua.yu@intel.com
Cc: peterz@infradead.org
Cc: eranian@google.com
Cc: vikas.shivappa@intel.com
Cc: ak@linux.intel.com
Cc: davidcc@google.com
Cc: reinette.chatre@intel.com
Link: http://lkml.kernel.org/r/1501017287-28083-16-git-send-email-vikas.shivappa@linux.intel.com

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -314,6 +314,7 @@ static void move_myself(struct callback_head *head)
 	if (atomic_dec_and_test(&rdtgrp->waitcount) &&
 	    (rdtgrp->flags & RDT_DELETED)) {
 		current->closid = 0;
+		current->rmid = 0;
 		kfree(rdtgrp);
 	}
 
@@ -352,7 +353,20 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 		atomic_dec(&rdtgrp->waitcount);
 		kfree(callback);
 	} else {
+		/*
+		 * For ctrl_mon groups move both closid and rmid.
+		 * For monitor groups, can move the tasks only from
+		 * their parent CTRL group.
+		 */
+		if (rdtgrp->type == RDTCTRL_GROUP) {
 			tsk->closid = rdtgrp->closid;
+			tsk->rmid = rdtgrp->mon.rmid;
+		} else if (rdtgrp->type == RDTMON_GROUP) {
+			if (rdtgrp->mon.parent->closid == tsk->closid)
+				tsk->rmid = rdtgrp->mon.rmid;
+			else
+				ret = -EINVAL;
+		}
 	}
 	return ret;
 }
@@ -432,7 +446,8 @@ static void show_rdt_tasks(struct rdtgroup *r, struct seq_file *s)
 
 	rcu_read_lock();
 	for_each_process_thread(p, t) {
-		if (t->closid == r->closid)
+		if ((r->type == RDTCTRL_GROUP && t->closid == r->closid) ||
+		    (r->type == RDTMON_GROUP && t->rmid == r->mon.rmid))
 			seq_printf(s, "%d\n", t->pid);
 	}
 	rcu_read_unlock();

include/linux/sched.h

@@ -900,6 +900,7 @@ struct task_struct {
 #endif
 #ifdef CONFIG_INTEL_RDT
 	u32				closid;
+	u32				rmid;
 #endif
 #ifdef CONFIG_FUTEX
 	struct robust_list_head __user	*robust_list;