diff --git a/arch/x86_64/kernel/syscall.c b/arch/x86_64/kernel/syscall.c
index 2f5f8a58..4b87d1f7 100644
--- a/arch/x86_64/kernel/syscall.c
+++ b/arch/x86_64/kernel/syscall.c
@@ -1329,15 +1329,20 @@ done:
 		mcs_rwlock_reader_lock_noirq(&tproc->update_lock, &updatelock);
 		savelock = &tthread->sigpendinglock;
 		head = &tthread->sigpending;
-		if(sig == SIGKILL ||
-		   (tproc->status != PS_EXITED &&
-		    tproc->status != PS_ZOMBIE &&
-		    tthread->status != PS_EXITED)){
+		mcs_rwlock_reader_lock_noirq(&tproc->threads_lock, &lock);
+		if (tthread->status != PS_EXITED &&
+			(sig == SIGKILL ||
+			 (tproc->status != PS_EXITED && tproc->status != PS_ZOMBIE))) {
 			hold_thread(tthread);
+			if ((rc = hold_thread(tthread))) {
+				kprintf("%s: ERROR hold_thread returned %d,tid=%d\n", __FUNCTION__, rc, tthread->tid);
+				tthread = NULL;
+			}
 		}
 		else{
 			tthread = NULL;
 		}
+		mcs_rwlock_reader_unlock_noirq(&tproc->threads_lock, &lock);
 		mcs_rwlock_reader_unlock_noirq(&tproc->update_lock, &updatelock);
 		mcs_rwlock_reader_unlock_noirq(&thash->lock[hash], &lock);
 	}
diff --git a/kernel/include/process.h b/kernel/include/process.h
index 7c0b6f74..8eb8142c 100644
--- a/kernel/include/process.h
+++ b/kernel/include/process.h
@@ -575,9 +575,6 @@ struct process {
 	int nr_processes; /* For partitioned execution */
 };
 
-void hold_thread(struct thread *ftn);
-void release_thread(struct thread *ftn);
-
 /*
  * Scheduling policies
  */
@@ -753,7 +750,7 @@ struct thread *create_thread(unsigned long user_pc,
 struct thread *clone_thread(struct thread *org, unsigned long pc,
                               unsigned long sp, int clone_flags);
 void destroy_thread(struct thread *thread);
-void hold_thread(struct thread *thread);
+int hold_thread(struct thread *thread);
 void release_thread(struct thread *thread);
 void flush_process_memory(struct process_vm *vm);
 void hold_process_vm(struct process_vm *vm);
diff --git a/kernel/process.c b/kernel/process.c
index 81856187..3a5da9f3 100644
--- a/kernel/process.c
+++ b/kernel/process.c
@@ -2571,14 +2571,15 @@ out:
 	return error;
 }
 
-void hold_thread(struct thread *thread)
+int hold_thread(struct thread *thread)
 {
 	if (thread->status == PS_EXITED) {
-		panic("hold_thread: already exited process");
+		kprintf("hold_thread: ERROR: already exited process,tid=%d\n", thread->tid);
+		return -ESRCH;
 	}
 
 	ihk_atomic_inc(&thread->refcount);
-	return;
+	return 0;
 }
 
 void
diff --git a/kernel/syscall.c b/kernel/syscall.c
index f462c636..b8682fc4 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -1004,13 +1004,13 @@ void terminate(int rc, int sig)
 		sync_child_event(proc->monitoring_event);
 
 	// clean up threads
-	mcs_rwlock_reader_lock(&proc->threads_lock, &lock); // conflict clone
+	mcs_rwlock_writer_lock(&proc->threads_lock, &lock); // conflict clone
 	mcs_rwlock_writer_lock_noirq(&proc->update_lock, &updatelock);
 	if (proc->status == PS_EXITED) {
-		mcs_rwlock_writer_unlock_noirq(&proc->update_lock, &updatelock);
-		mcs_rwlock_reader_unlock(&proc->threads_lock, &lock);
 		preempt_disable();
 		mythread->status = PS_EXITED;
+		mcs_rwlock_writer_unlock_noirq(&proc->update_lock, &updatelock);
+		mcs_rwlock_writer_unlock(&proc->threads_lock, &lock);
 		release_thread(mythread);
 		preempt_enable();
 		schedule();
@@ -1021,10 +1021,10 @@ void terminate(int rc, int sig)
 	exit_status = ((rc & 0x00ff) << 8) | (sig & 0xff);
 	mythread->exit_status = exit_status;
 	proc->status = PS_EXITED;
-	terminate_mcexec(rc, sig);
-
 	mcs_rwlock_writer_unlock_noirq(&proc->update_lock, &updatelock);
-	mcs_rwlock_reader_unlock(&proc->threads_lock, &lock);
+	mcs_rwlock_writer_unlock(&proc->threads_lock, &lock);
+
+	terminate_mcexec(rc, sig);
 
 	mcs_rwlock_writer_lock(&proc->threads_lock, &lock);
 	list_del(&mythread->siblings_list);
@@ -1174,7 +1174,9 @@ void terminate(int rc, int sig)
 	finalize_process(proc);
 
 	preempt_disable();
+	mcs_rwlock_writer_lock(&proc->threads_lock, &lock);
 	mythread->status = PS_EXITED;
+	mcs_rwlock_writer_unlock(&proc->threads_lock, &lock);
 	release_thread(mythread);
 	release_process_vm(vm);
 	preempt_enable();
@@ -5475,16 +5477,16 @@ do_exit(int code)
 		      FUTEX_WAKE, 1, 0, NULL, 0, 0, 1);
 	}
 
-	mcs_rwlock_reader_lock(&proc->threads_lock, &lock);
+	mcs_rwlock_writer_lock(&proc->threads_lock, &lock);
 	if(proc->status == PS_EXITED){
-		mcs_rwlock_reader_unlock(&proc->threads_lock, &lock);
+		mcs_rwlock_writer_unlock(&proc->threads_lock, &lock);
 		terminate(exit_status, 0);
 		return;
 	}
 	preempt_disable();
 	thread->status = PS_EXITED;
 	sync_child_event(thread->proc->monitoring_event);
-	mcs_rwlock_reader_unlock(&proc->threads_lock, &lock);
+	mcs_rwlock_writer_unlock(&proc->threads_lock, &lock);
 	release_thread(thread);
 	preempt_enable();