[PATCH 3/5] x86/intel_rdt: Add diagnostics when writing the tasks file

["Luck, Tony" <tony.luck@intel.com>]

From: Tony Luck <tony.luck@intel.com>

About the only tricky case is trying to move a task into a monitor
group that is a subdirectory of a different control group. But cover
the simple cases too.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index 6a2cd89fa9de..c54189a1b54e 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -455,6 +455,7 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 		 */
 		atomic_dec(&rdtgrp->waitcount);
 		kfree(callback);
+		seq_buf_puts(&last_cmd_status, "task exited\n");
 	} else {
 		/*
 		 * For ctrl_mon groups move both closid and rmid.
@@ -465,10 +466,13 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 			tsk->closid = rdtgrp->closid;
 			tsk->rmid = rdtgrp->mon.rmid;
 		} else if (rdtgrp->type == RDTMON_GROUP) {
-			if (rdtgrp->mon.parent->closid == tsk->closid)
+			if (rdtgrp->mon.parent->closid == tsk->closid) {
 				tsk->rmid = rdtgrp->mon.rmid;
-			else
+			} else {
+				seq_buf_puts(&last_cmd_status,
+					     "Can't move task to different control group\n");
 				ret = -EINVAL;
+			}
 		}
 	}
 	return ret;
@@ -487,8 +491,11 @@ static int rdtgroup_task_write_permission(struct task_struct *task,
 	 */
 	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
 	    !uid_eq(cred->euid, tcred->uid) &&
-	    !uid_eq(cred->euid, tcred->suid))
+	    !uid_eq(cred->euid, tcred->suid)) {
+		seq_buf_printf(&last_cmd_status,
+			       "No permission to move task %d\n", task->pid);
 		ret = -EPERM;
+	}
 
 	put_cred(tcred);
 	return ret;
@@ -505,6 +512,7 @@ static int rdtgroup_move_task(pid_t pid, struct rdtgroup *rdtgrp,
 		tsk = find_task_by_vpid(pid);
 		if (!tsk) {
 			rcu_read_unlock();
+			seq_buf_printf(&last_cmd_status, "No task %d\n", pid);
 			return -ESRCH;
 		}
 	} else {
@@ -532,6 +540,7 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
 		return -EINVAL;
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
+	seq_buf_clear(&last_cmd_status);
 
 	if (rdtgrp)
 		ret = rdtgroup_move_task(pid, rdtgrp, of);
-- 
2.11.0