[PATCH v2 3/6] 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_ctrlmondata.c |  4 +---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c    | 15 +++++++++++----
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
index f29b4c21e7d4..30aeb267cbd2 100644
--- a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
@@ -232,10 +232,8 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 	int closid, ret = 0;
 
 	/* Valid input requires a trailing newline */
-	if (nbytes == 0 || buf[nbytes - 1] != '\n') {
-		seq_buf_puts(&last_cmd_status, "no trailing newline\n");
+	if (nbytes == 0 || buf[nbytes - 1] != '\n')
 		return -EINVAL;
-	}
 	buf[nbytes - 1] = '\0';
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index 9268122eb149..df6373680a59 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -478,6 +478,7 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 		 */
 		atomic_dec(&rdtgrp->waitcount);
 		kfree(callback);
+		rdt_last_cmd_puts("task exited\n");
 	} else {
 		/*
 		 * For ctrl_mon groups move both closid and rmid.
@@ -488,10 +489,12 @@ 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 {
+				rdt_last_cmd_puts("Can't move task to different control group\n");
 				ret = -EINVAL;
+			}
 		}
 	}
 	return ret;
@@ -510,8 +513,10 @@ 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)) {
+		rdt_last_cmd_printf("No permission to move task %d\n", task->pid);
 		ret = -EPERM;
+	}
 
 	put_cred(tcred);
 	return ret;
@@ -528,6 +533,7 @@ static int rdtgroup_move_task(pid_t pid, struct rdtgroup *rdtgrp,
 		tsk = find_task_by_vpid(pid);
 		if (!tsk) {
 			rcu_read_unlock();
+			rdt_last_cmd_printf("No task %d\n", pid);
 			return -ESRCH;
 		}
 	} else {
@@ -555,6 +561,7 @@ 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);
+	rdt_last_cmd_clear();
 
 	if (rdtgrp)
 		ret = rdtgroup_move_task(pid, rdtgrp, of);
@@ -1208,7 +1215,7 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
 out_cdp:
 	cdp_disable();
 out:
-	seq_buf_clear(&last_cmd_status);
+	rdt_last_cmd_clear();
 	mutex_unlock(&rdtgroup_mutex);
 
 	return dentry;
-- 
2.11.0