function-graph: add memory barriers for accessing task's ret_stack

The code that handles the tasks ret_stack allocation for every task
assumes that only an interrupt can cause issues (even though interrupts
are disabled).

In reality, the code is allocating the ret_stack for tasks that may be
running on other CPUs and there are not efficient memory barriers to
handle this case.

[ Impact: prevent crash due to using of uninitialized ret_stack variables ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 20e066065eb3..1664d3f33d38 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2580,12 +2580,12 @@ 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);