diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 207ea4734384d0771cc04897a43a30779a78f29c..1adec072b04849380de6592be5ed3bbfc1a21307 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -1285,6 +1285,8 @@ EXPORT_SYMBOL(ptrace_pre_hook);
 SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
 		unsigned long, data)
 {
+	int (*hook)(long request, long pid, struct task_struct *task, long addr,
+		    long data);
 	struct task_struct *child;
 	long ret;
 
@@ -1299,11 +1301,21 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
 		goto out;
 	}
 
-	if (ptrace_pre_hook) {
-		ret = ptrace_pre_hook(request, pid, child, addr, data);
-		if (ret)
+	/*
+	 * The hook is provided by a loadable module and disappears when that
+	 * module is unloaded, so the call has to be inside an RCU read-side
+	 * critical section; the unload path waits for a grace period.
+	 */
+	rcu_read_lock();
+	hook = READ_ONCE(ptrace_pre_hook);
+	if (hook) {
+		ret = hook(request, pid, child, addr, data);
+		if (ret) {
+			rcu_read_unlock();
 			goto out_put_task_struct;
+		}
 	}
+	rcu_read_unlock();
 
 	if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
 		ret = ptrace_attach(child, request, addr, data);
@@ -1430,6 +1442,8 @@ int compat_ptrace_request(struct task_struct *child, compat_long_t request,
 COMPAT_SYSCALL_DEFINE4(ptrace, compat_long_t, request, compat_long_t, pid,
 		       compat_long_t, addr, compat_long_t, data)
 {
+	int (*hook)(long request, long pid, struct task_struct *task, long addr,
+		    long data);
 	struct task_struct *child;
 	long ret;
 
@@ -1444,11 +1458,21 @@ COMPAT_SYSCALL_DEFINE4(ptrace, compat_long_t, request, compat_long_t, pid,
 		goto out;
 	}
 
-	if (ptrace_pre_hook) {
-		ret = ptrace_pre_hook(request, pid, child, addr, data);
-		if (ret)
+	/*
+	 * The hook is provided by a loadable module and disappears when that
+	 * module is unloaded, so the call has to be inside an RCU read-side
+	 * critical section; the unload path waits for a grace period.
+	 */
+	rcu_read_lock();
+	hook = READ_ONCE(ptrace_pre_hook);
+	if (hook) {
+		ret = hook(request, pid, child, addr, data);
+		if (ret) {
+			rcu_read_unlock();
 			goto out_put_task_struct;
+		}
 	}
+	rcu_read_unlock();
 
 	if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
 		ret = ptrace_attach(child, request, addr, data);
diff --git a/kernel/tkernel/ttools/ttools_module.c b/kernel/tkernel/ttools/ttools_module.c
index e1302187a15b18f9971f54ea7344d8c6666abb8b..385eeaf70e2dc49524c42d39ba68edc1b8fd2853 100644
--- a/kernel/tkernel/ttools/ttools_module.c
+++ b/kernel/tkernel/ttools/ttools_module.c
@@ -258,7 +258,7 @@ static int ttools_init(void)
 	if (ret)
 		return ret;
 
-	ptrace_pre_hook = ttools_ptrace_hook;
+	WRITE_ONCE(ptrace_pre_hook, ttools_ptrace_hook);
 	smp_wmb();
 	smp_call_function(flush_icache_1, NULL, 1);
 	pr_info("ttools " TTOOLS_VER " loaded\n");
@@ -267,9 +267,11 @@ static int ttools_init(void)
 
 static void ttools_exit(void)
 {
-	ptrace_pre_hook = NULL;
+	WRITE_ONCE(ptrace_pre_hook, NULL);
 	smp_wmb();
 	smp_call_function(flush_icache_1, NULL, 1);
+	/* wait for callers which are still inside the hook */
+	synchronize_rcu();
 	misc_deregister(&ttools_dev);
 	ttools_clean_task_list();
 	pr_info("ttools " TTOOLS_VER " unloaded\n");