1 files changed, 19 insertions, 10 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d6973dfadb36..bb60732ade0c 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3218,12 +3218,12 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
                 }
 
                 if (t->ret_stack == NULL) {
-                        t->curr_ret_stack = -1;
-                        /* Make sure IRQs see the -1 first: */
-                        barrier();
-                        t->ret_stack = ret_stack_list[start++];
                         atomic_set(&t->tracing_graph_pause, 0);
                         atomic_set(&t->trace_overrun, 0);
+                        t->curr_ret_stack = -1;
+                        /* Make sure the tasks see the -1 first: */
+                        smp_wmb();
+                        t->ret_stack = ret_stack_list[start++];
                 }
         } while_each_thread(g, t);
 
@@ -3281,8 +3281,10 @@ static int start_graph_tracing(void)
                 return -ENOMEM;
 
         /* The cpu_boot init_task->ret_stack will never be freed */
-        for_each_online_cpu(cpu)
-                ftrace_graph_init_task(idle_task(cpu));
+        for_each_online_cpu(cpu) {
+                if (!idle_task(cpu)->ret_stack)
+                        ftrace_graph_init_task(idle_task(cpu));
+        }
 
         do {
                 ret = alloc_retstack_tasklist(ret_stack_list);
@@ -3374,18 +3376,25 @@ void unregister_ftrace_graph(void)
 /* Allocate a return stack for newly created task */
 void ftrace_graph_init_task(struct task_struct *t)
 {
+        /* Make sure we do not use the parent ret_stack */
+        t->ret_stack = NULL;
+
         if (ftrace_graph_active) {
-                t->ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
+                struct ftrace_ret_stack *ret_stack;
+
+                ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
                                 * sizeof(struct ftrace_ret_stack),
                                 GFP_KERNEL);
-                if (!t->ret_stack)
+                if (!ret_stack)
                         return;
                 t->curr_ret_stack = -1;
                 atomic_set(&t->tracing_graph_pause, 0);
                 atomic_set(&t->trace_overrun, 0);
                 t->ftrace_timestamp = 0;
-        } else
-                t->ret_stack = NULL;
+                /* make curr_ret_stack visable before we add the ret_stack */
+                smp_wmb();
+                t->ret_stack = ret_stack;
+        }
 }
 
 void ftrace_graph_exit_task(struct task_struct *t)