1 files changed, 32 insertions, 18 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index fc21312dad6d..17b95a492948 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -490,16 +490,6 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
         } else if (ops->flags & FTRACE_OPS_FL_CONTROL) {
                 ret = remove_ftrace_list_ops(&ftrace_control_list,
                                              &control_ops, ops);
-                if (!ret) {
-                        /*
-                         * The ftrace_ops is now removed from the list,
-                         * so there'll be no new users. We must ensure
-                         * all current users are done before we free
-                         * the control data.
-                         */
-                        synchronize_sched();
-                        control_ops_free(ops);
-                }
         } else
                 ret = remove_ftrace_ops(&ftrace_ops_list, ops);
 
@@ -509,13 +499,6 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
         if (ftrace_enabled)
                 update_ftrace_function();
 
-        /*
-         * Dynamic ops may be freed, we must make sure that all
-         * callers are done before leaving this function.
-         */
-        if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
-                synchronize_sched();
-
         return 0;
 }
 
@@ -2184,10 +2167,41 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
                 command |= FTRACE_UPDATE_TRACE_FUNC;
         }
 
-        if (!command || !ftrace_enabled)
+        if (!command || !ftrace_enabled) {
+                /*
+                 * If these are control ops, they still need their
+                 * per_cpu field freed. Since, function tracing is
+                 * not currently active, we can just free them
+                 * without synchronizing all CPUs.
+                 */
+                if (ops->flags & FTRACE_OPS_FL_CONTROL)
+                        control_ops_free(ops);
                 return 0;
+        }
 
         ftrace_run_update_code(command);
+
+        /*
+         * Dynamic ops may be freed, we must make sure that all
+         * callers are done before leaving this function.
+         * The same goes for freeing the per_cpu data of the control
+         * ops.
+         *
+         * Again, normal synchronize_sched() is not good enough.
+         * We need to do a hard force of sched synchronization.
+         * This is because we use preempt_disable() to do RCU, but
+         * the function tracers can be called where RCU is not watching
+         * (like before user_exit()). We can not rely on the RCU
+         * infrastructure to do the synchronization, thus we must do it
+         * ourselves.
+         */
+        if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_CONTROL)) {
+                schedule_on_each_cpu(ftrace_sync);
+
+                if (ops->flags & FTRACE_OPS_FL_CONTROL)
+                        control_ops_free(ops);
+        }
+
         return 0;
 }