diff --git a/include/kernel/mr_ktimer.h b/include/kernel/mr_ktimer.h
index 02c9697..c52163f 100644
--- a/include/kernel/mr_ktimer.h
+++ b/include/kernel/mr_ktimer.h
@@ -25,7 +25,7 @@ extern "C" {
  */
 
 #if defined(MR_USE_KTIMER)
-/* Periodic definition */
+/* Ktimer periodic definition */
 #define MR_KTIMER_PERIODIC              (1U << 31)
 
 /* Ktimer type */
@@ -61,13 +61,13 @@ mr_err_t mr_ktimer_init(mr_ktimer_t *ktimer, const char *name,
                         void *args, mr_tick_t tick);
 
 /**
- * @brief This function create a timer.
+ * @brief This function create a ktimer.
  *
- * @param name The timer name.
- * @param entry The timer entry.
- * @param args The timer args.
- * @param tick The timer tick.
- * @return The timer on success, or MR_NULL on failure.
+ * @param name The ktimer name.
+ * @param entry The ktimer entry.
+ * @param args The ktimer args.
+ * @param tick The ktimer tick.
+ * @return The ktimer on success, or MR_NULL on failure.
  */
 mr_ktimer_t *mr_ktimer_create(const char *name,
                               void (*entry)(mr_ktimer_t *ktimer, void *args),
@@ -108,6 +108,16 @@ mr_err_t mr_ktimer_stop(mr_ktimer_t *ktimer);
  */
 mr_err_t mr_ktimer_tick_set(mr_ktimer_t *ktimer, mr_tick_t tick);
 
+/**
+ * @brief This function check if a ktimer is running.
+ *
+ * @param ktimer The ktimer.
+ * @return MR_TRUE if the ktimer is running, MR_FALSE otherwise.
+ */
+MR_INLINE mr_bool_t mr_ktimer_is_running(mr_ktimer_t *ktimer) {
+    return mr_klist_is_empty(&ktimer->list);
+}
+
 /**
  * @brief This function find a ktimer.
  *
diff --git a/include/mr_x.h b/include/mr_x.h
index f59188b..422473f 100644
--- a/include/mr_x.h
+++ b/include/mr_x.h
@@ -16,6 +16,7 @@
 
 #include <kernel/mr_initcall.h>
 #include <kernel/mr_kclock.h>
+#include <kernel/mr_kfifo.h>
 #include <kernel/mr_khook.h>
 #include <kernel/mr_klist.h>
 #include <kernel/mr_kobject.h>
diff --git a/kernel/kobject.c b/kernel/kobject.c
index ba97658..cd32ed4 100644
--- a/kernel/kobject.c
+++ b/kernel/kobject.c
@@ -235,16 +235,9 @@ MR_INLINE mr_err_t kobject_add(mr_kobject_t *kobj, mr_kobject_t *parent,
         return -MR_EEXIST;
     }
 
-    /* Get parent */
-    parent = mr_kobject_get(parent);
-    if (!parent) {
-        return -MR_ENOENT;
-    }
-
     /* Allocate name */
     ret = kobject_name_alloc(kobj, path);
     if (ret != 0) {
-        mr_kobject_put(parent);
         return ret;
     }
 
@@ -261,6 +254,12 @@ MR_INLINE mr_err_t kobject_add_varg(mr_kobject_t *kobj, mr_kobject_t *parent,
     mr_err_t ret;
     int mask;
 
+    /* Get parent */
+    parent = mr_kobject_get(parent);
+    if (!parent) {
+        return -MR_EINVAL;
+    }
+
     /* Lock */
     mask = mr_kspinlock_lock_irqsave(&klock);
 
@@ -284,6 +283,11 @@ MR_INLINE mr_err_t kobject_add_varg(mr_kobject_t *kobj, mr_kobject_t *parent,
 _exit:
     /* Unlock */
     mr_kspinlock_unlock_irqrestore(&klock, mask);
+
+    /* Put parent */
+    if (ret != 0) {
+        mr_kobject_put(parent);
+    }
     return ret;
 }
 
@@ -311,14 +315,12 @@ MR_INLINE void kobject_del(mr_kobject_t *kobj) {
     /* Lock */
     mask = mr_kspinlock_lock_irqsave(&klock);
 
-    /* Already deleted */
-    if (mr_klist_is_empty(&kobj->entry)) {
-        goto _exit;
+    /* Check kobject is deleted */
+    if (!mr_klist_is_empty(&kobj->entry)) {
+        /* Remove kobject from parent */
+        mr_klist_del(&kobj->entry);
     }
 
-    /* Remove kobject from parent */
-    mr_klist_del(&kobj->entry);
-_exit:
     /* Unlock */
     mr_kspinlock_unlock_irqrestore(&klock, mask);
 }
@@ -344,6 +346,12 @@ MR_INLINE mr_kobject_t *kobject_lookup_varg(mr_kobject_t *parent,
     mr_err_t ret;
     int mask;
 
+    /* Get parent */
+    parent = mr_kobject_get(parent);
+    if (!parent) {
+        return MR_NULL;
+    }
+
     /* Lock */
     mask = mr_kspinlock_lock_irqsave(&klock);
 
@@ -365,6 +373,9 @@ MR_INLINE mr_kobject_t *kobject_lookup_varg(mr_kobject_t *parent,
 _exit:
     /* Unlock */
     mr_kspinlock_unlock_irqrestore(&klock, mask);
+
+    /* Put parent */
+    mr_kobject_put(parent);
     return kobj;
 }
 
diff --git a/kernel/ktimer.c b/kernel/ktimer.c
index daffc00..3dc689d 100644
--- a/kernel/ktimer.c
+++ b/kernel/ktimer.c
@@ -94,8 +94,9 @@ MR_INLINE void ktimer_del(mr_ktimer_t *ktimer) {
     /* Lock */
     mask = mr_kspinlock_lock_irqsave(&klock);
 
-    /* Remove ktimer from ktimer list */
+    /* Check ktimer is deleted */
     if (!mr_klist_is_empty(&ktimer->list)) {
+        /* Remove ktimer from timer list */
         mr_klist_del(&ktimer->list);
     }
 
@@ -118,15 +119,15 @@ mr_err_t mr_ktimer_del(mr_ktimer_t *ktimer) {
 }
 
 MR_INLINE void ktimer_insert(mr_ktimer_t *ktimer) {
-    mr_tick_t tick;
     mr_ktimer_t *t;
+    mr_tick_t tick;
     mr_klist_t *l;
 
     /* Set timeout tick */
     tick = ktimer->init_tick & ~MR_KTIMER_PERIODIC;
     ktimer->timeout_tick = mr_kclock_tick() + tick;
 
-    /* Insert ktimer into ktimer list */
+    /* Insert ktimer into timer list */
     MR_KLIST_FOR_EACH(l, &klist) {
         t = MR_KLIST_ENTRY(l, mr_ktimer_t, list);
         if ((ktimer->timeout_tick - t->timeout_tick) < (MR_TICK_MAX / 2)) {
@@ -148,7 +149,7 @@ MR_INLINE void ktimer_start(mr_ktimer_t *ktimer) {
     /* Lock */
     mask = mr_kspinlock_lock_irqsave(&klock);
 
-    /* Insert ktimer into ktimer list */
+    /* Insert ktimer into timer list */
     ktimer_insert(ktimer);
 
     /* Unlock */
@@ -183,7 +184,7 @@ MR_INLINE void ktimer_tick_set(mr_ktimer_t *ktimer, mr_tick_t tick) {
     /* Lock */
     mask = mr_kspinlock_lock_irqsave(&klock);
 
-    /* Remove ktimer from ktimer list */
+    /* Remove ktimer from timer list */
     if (!mr_klist_is_empty(&ktimer->list)) {
         mr_klist_del(&ktimer->list);
     }