diff --git a/sched/sched/sched_waitid.c b/sched/sched/sched_waitid.c
index b8fb630b9c3..20019342af1 100644
--- a/sched/sched/sched_waitid.c
+++ b/sched/sched/sched_waitid.c
@@ -143,6 +143,14 @@ int nx_waitid(int idtype, id_t id, FAR siginfo_t *info, int options)
   sigemptyset(&set);
   nxsig_addset(&set, SIGCHLD);
 
+  /* NOTE: sched_lock() is not enough for SMP
+   * because the child task is running on another CPU
+   */
+
+#ifdef CONFIG_SMP
+  irqstate_t flags = enter_critical_section();
+#endif
+
   /* Disable pre-emption so that nothing changes while the loop executes */
 
   sched_lock();
@@ -379,6 +387,11 @@ int nx_waitid(int idtype, id_t id, FAR siginfo_t *info, int options)
 
 errout:
   sched_unlock();
+
+#ifdef CONFIG_SMP
+  leave_critical_section(flags);
+#endif
+
   return ret;
 }
 
diff --git a/sched/sched/sched_waitpid.c b/sched/sched/sched_waitpid.c
index b23a68ecd95..0dd7de6ca51 100644
--- a/sched/sched/sched_waitpid.c
+++ b/sched/sched/sched_waitpid.c
@@ -72,6 +72,14 @@ pid_t nx_waitpid(pid_t pid, int *stat_loc, int options)
 
   DEBUGASSERT(stat_loc);
 
+  /* NOTE: sched_lock() is not enough for SMP
+   * because the child task is running on another CPU
+   */
+
+#ifdef CONFIG_SMP
+  irqstate_t flags = enter_critical_section();
+#endif
+
   /* Disable pre-emption so that nothing changes in the following tests */
 
   sched_lock();
@@ -158,11 +166,15 @@ pid_t nx_waitpid(pid_t pid, int *stat_loc, int options)
 
   /* On success, return the PID */
 
-  sched_unlock();
-  return pid;
+  ret = pid;
 
 errout:
   sched_unlock();
+
+#ifdef CONFIG_SMP
+  leave_critical_section(flags);
+#endif
+
   return ret;
 }
 
@@ -199,6 +211,14 @@ pid_t nx_waitpid(pid_t pid, int *stat_loc, int options)
   sigemptyset(&set);
   nxsig_addset(&set, SIGCHLD);
 
+  /* NOTE: sched_lock() is not enough for SMP
+   * because the child task is running on another CPU
+   */
+
+#ifdef CONFIG_SMP
+  irqstate_t flags = enter_critical_section();
+#endif
+
   /* Disable pre-emption so that nothing changes while the loop executes */
 
   sched_lock();
@@ -438,11 +458,17 @@ pid_t nx_waitpid(pid_t pid, int *stat_loc, int options)
         }
     }
 
-  sched_unlock();
-  return pid;
+  /* On success, return the PID */
+
+  ret = pid;
 
 errout:
   sched_unlock();
+
+#ifdef CONFIG_SMP
+  leave_critical_section(flags);
+#endif
+
   return ret;
 }
 #endif /* CONFIG_SCHED_HAVE_PARENT */
diff --git a/sched/task/task_exithook.c b/sched/task/task_exithook.c
index 8b9ff31d8dd..9b9477c0f32 100644
--- a/sched/task/task_exithook.c
+++ b/sched/task/task_exithook.c
@@ -634,6 +634,12 @@ void nxtask_exithook(FAR struct tcb_s *tcb, int status, bool nonblocking)
 
   nxtask_recover(tcb);
 
+  /* NOTE: signal handling needs to be done in a criticl section */
+
+#ifdef CONFIG_SMP
+  irqstate_t flags = enter_critical_section();
+#endif
+
   /* Send the SIGCHLD signal to the parent task group */
 
   nxtask_signalparent(tcb, status);
@@ -668,6 +674,10 @@ void nxtask_exithook(FAR struct tcb_s *tcb, int status, bool nonblocking)
 
   nxsig_cleanup(tcb); /* Deallocate Signal lists */
 
+#ifdef CONFIG_SMP
+  leave_critical_section(flags);
+#endif
+
   /* This function can be re-entered in certain cases.  Set a flag
    * bit in the TCB to not that we have already completed this exit
    * processing.