2 files changed, 26 insertions, 0 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index ca17c20a1010..4cfeca6ffe11 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -913,6 +913,14 @@ void *arch_ftrace_trampoline_func(struct ftrace_ops *ops, struct dyn_ftrace *rec
         return addr_from_call((void *)ops->trampoline + offset);
 }
 
+void arch_ftrace_trampoline_free(struct ftrace_ops *ops)
+{
+        if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
+                return;
+
+        tramp_free((void *)ops->trampoline);
+        ops->trampoline = 0;
+}
 
 #endif /* CONFIG_X86_64 */
 #endif /* CONFIG_DYNAMIC_FTRACE */
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 422e1f8300b1..eab3123a1fbe 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2324,6 +2324,10 @@ static void ftrace_run_modify_code(struct ftrace_ops *ops, int command,
 static ftrace_func_t saved_ftrace_func;
 static int ftrace_start_up;
 
+void __weak arch_ftrace_trampoline_free(struct ftrace_ops *ops)
+{
+}
+
 static void control_ops_free(struct ftrace_ops *ops)
 {
         free_percpu(ops->disabled);
@@ -2475,6 +2479,8 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
         if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_CONTROL)) {
                 schedule_on_each_cpu(ftrace_sync);
 
+                arch_ftrace_trampoline_free(ops);
+
                 if (ops->flags & FTRACE_OPS_FL_CONTROL)
                         control_ops_free(ops);
         }
@@ -4725,9 +4731,21 @@ void __weak arch_ftrace_update_trampoline(struct ftrace_ops *ops)
 
 static void ftrace_update_trampoline(struct ftrace_ops *ops)
 {
+
+/*
+ * Currently there's no safe way to free a trampoline when the kernel
+ * is configured with PREEMPT. That is because a task could be preempted
+ * when it jumped to the trampoline, it may be preempted for a long time
+ * depending on the system load, and currently there's no way to know
+ * when it will be off the trampoline. If the trampoline is freed
+ * too early, when the task runs again, it will be executing on freed
+ * memory and crash.
+ */
+#ifdef CONFIG_PREEMPT
         /* Currently, only non dynamic ops can have a trampoline */
         if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
                 return;
+#endif
 
         arch_ftrace_update_trampoline(ops);
 }