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/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f212da4..90d99fb 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1498,10 +1498,77 @@
#ifdef CONFIG_FUNCTION_RET_TRACER
+static atomic_t ftrace_retfunc_active;
+
/* The callback that hooks the return of a function */
trace_function_return_t ftrace_function_return =
(trace_function_return_t)ftrace_stub;
+
+/* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
+static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
+{
+ int i;
+ int ret = 0;
+ unsigned long flags;
+ int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE;
+ struct task_struct *g, *t;
+
+ for (i = 0; i < FTRACE_RETSTACK_ALLOC_SIZE; i++) {
+ ret_stack_list[i] = kmalloc(FTRACE_RETFUNC_DEPTH
+ * sizeof(struct ftrace_ret_stack),
+ GFP_KERNEL);
+ if (!ret_stack_list[i]) {
+ start = 0;
+ end = i;
+ ret = -ENOMEM;
+ goto free;
+ }
+ }
+
+ read_lock_irqsave(&tasklist_lock, flags);
+ do_each_thread(g, t) {
+ if (start == end) {
+ ret = -EAGAIN;
+ goto unlock;
+ }
+
+ if (t->ret_stack == NULL) {
+ t->ret_stack = ret_stack_list[start++];
+ t->curr_ret_stack = -1;
+ atomic_set(&t->trace_overrun, 0);
+ }
+ } while_each_thread(g, t);
+
+unlock:
+ read_unlock_irqrestore(&tasklist_lock, flags);
+free:
+ for (i = start; i < end; i++)
+ kfree(ret_stack_list[i]);
+ return ret;
+}
+
+/* Allocate a return stack for each task */
+static int start_return_tracing(void)
+{
+ struct ftrace_ret_stack **ret_stack_list;
+ int ret;
+
+ ret_stack_list = kmalloc(FTRACE_RETSTACK_ALLOC_SIZE *
+ sizeof(struct ftrace_ret_stack *),
+ GFP_KERNEL);
+
+ if (!ret_stack_list)
+ return -ENOMEM;
+
+ do {
+ ret = alloc_retstack_tasklist(ret_stack_list);
+ } while (ret == -EAGAIN);
+
+ kfree(ret_stack_list);
+ return ret;
+}
+
int register_ftrace_return(trace_function_return_t func)
{
int ret = 0;
@@ -1516,7 +1583,12 @@
ret = -EBUSY;
goto out;
}
-
+ atomic_inc(&ftrace_retfunc_active);
+ ret = start_return_tracing();
+ if (ret) {
+ atomic_dec(&ftrace_retfunc_active);
+ goto out;
+ }
ftrace_tracing_type = FTRACE_TYPE_RETURN;
ftrace_function_return = func;
ftrace_startup();
@@ -1530,6 +1602,7 @@
{
mutex_lock(&ftrace_sysctl_lock);
+ atomic_dec(&ftrace_retfunc_active);
ftrace_function_return = (trace_function_return_t)ftrace_stub;
ftrace_shutdown();
/* Restore normal tracing type */
@@ -1537,6 +1610,27 @@
mutex_unlock(&ftrace_sysctl_lock);
}
+
+/* Allocate a return stack for newly created task */
+void ftrace_retfunc_init_task(struct task_struct *t)
+{
+ if (atomic_read(&ftrace_retfunc_active)) {
+ t->ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
+ * sizeof(struct ftrace_ret_stack),
+ GFP_KERNEL);
+ if (!t->ret_stack)
+ return;
+ t->curr_ret_stack = -1;
+ atomic_set(&t->trace_overrun, 0);
+ } else
+ t->ret_stack = NULL;
+}
+
+void ftrace_retfunc_exit_task(struct task_struct *t)
+{
+ kfree(t->ret_stack);
+ t->ret_stack = NULL;
+}
#endif