tracing/function-return-tracer: store return stack into task_struct and allocate it dynamically
Impact: use deeper function tracing depth safely
Some tests showed that function return tracing needed a more deeper depth
of function calls. But it could be unsafe to store these return addresses
to the stack.
So these arrays will now be allocated dynamically into task_struct of current
only when the tracer is activated.
Typical scheme when tracer is activated:
- allocate a return stack for each task in global list.
- fork: allocate the return stack for the newly created task
- exit: free return stack of current
- idle init: same as fork
I chose a default depth of 50. I don't have overruns anymore.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c8e0db4..bee1e93 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1352,6 +1352,17 @@
unsigned long default_timer_slack_ns;
struct list_head *scm_work_list;
+#ifdef CONFIG_FUNCTION_RET_TRACER
+ /* Index of current stored adress in ret_stack */
+ int curr_ret_stack;
+ /* Stack of return addresses for return function tracing */
+ struct ftrace_ret_stack *ret_stack;
+ /*
+ * Number of functions that haven't been traced
+ * because of depth overrun.
+ */
+ atomic_t trace_overrun;
+#endif
};
/*
@@ -2006,18 +2017,6 @@
{
*task_thread_info(p) = *task_thread_info(org);
task_thread_info(p)->task = p;
-
-#ifdef CONFIG_FUNCTION_RET_TRACER
- /*
- * When fork() creates a child process, this function is called.
- * But the child task may not inherit the return adresses traced
- * by the return function tracer because it will directly execute
- * in userspace and will not return to kernel functions its parent
- * used.
- */
- task_thread_info(p)->curr_ret_stack = -1;
- atomic_set(&task_thread_info(p)->trace_overrun, 0);
-#endif
}
static inline unsigned long *end_of_stack(struct task_struct *p)