function_graph: Reverse the order of pushing the ret_stack and the callback

The function graph profiler uses the ret_stack to store the "subtime" and
reuse it by nested functions and also on the return. But the current logic
has the profiler callback called before the ret_stack is updated, and it is
just modifying the ret_stack that will later be allocated (it's just lucky
that the "subtime" is not touched when it is allocated).

This could also cause a crash if we are at the end of the ret_stack when
this happens.

By reversing the order of the allocating the ret_stack and then calling the
callbacks attached to a function being traced, the ret_stack entry is no
longer used before it is allocated.

Cc: stable@kernel.org
Fixes: 03274a3ffb449 ("tracing/fgraph: Adjust fgraph depth before calling trace return callback")
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 4f0d72ae6362..2561460d7baf 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -188,15 +188,17 @@ int function_graph_enter(unsigned long ret, unsigned long func,
         trace.func = func;
         trace.depth = ++current->curr_ret_depth;
 
-        /* Only trace if the calling function expects to */
-        if (!ftrace_graph_entry(&trace))
-                goto out;
-
         if (ftrace_push_return_trace(ret, func,
                                      frame_pointer, retp))
                 goto out;
 
+        /* Only trace if the calling function expects to */
+        if (!ftrace_graph_entry(&trace))
+                goto out_ret;
+
         return 0;
+ out_ret:
+        current->curr_ret_stack--;
  out:
         current->curr_ret_depth--;
         return -EBUSY;