ftrace: add stack trace to function tracer
Impact: new feature to stack trace any function
Chris Mason asked about being able to pick and choose a function
and get a stack trace from it. This feature enables his request.
# echo io_schedule > /debug/tracing/set_ftrace_filter
# echo function > /debug/tracing/current_tracer
# echo func_stack_trace > /debug/tracing/trace_options
Produces the following in /debug/tracing/trace:
kjournald-702 [001] 135.673060: io_schedule <-sync_buffer
kjournald-702 [002] 135.673671:
<= sync_buffer
<= __wait_on_bit
<= out_of_line_wait_on_bit
<= __wait_on_buffer
<= sync_dirty_buffer
<= journal_commit_transaction
<= kjournald
Note, be careful about turning this on without filtering the functions.
You may find that you have a 10 second lag between typing and seeing
what you typed. This is why the stack trace for the function tracer
does not use the same stack_trace flag as the other tracers use.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 9236d7e..3a5fa08 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -16,6 +16,8 @@
#include "trace.h"
+static struct trace_array *func_trace;
+
static void start_function_trace(struct trace_array *tr)
{
tr->cpu = get_cpu();
@@ -34,6 +36,7 @@
static int function_trace_init(struct trace_array *tr)
{
+ func_trace = tr;
start_function_trace(tr);
return 0;
}
@@ -48,12 +51,93 @@
tracing_reset_online_cpus(tr);
}
+static void
+function_stack_trace_call(unsigned long ip, unsigned long parent_ip)
+{
+ struct trace_array *tr = func_trace;
+ struct trace_array_cpu *data;
+ unsigned long flags;
+ long disabled;
+ int cpu;
+ int pc;
+
+ if (unlikely(!ftrace_function_enabled))
+ return;
+
+ /*
+ * Need to use raw, since this must be called before the
+ * recursive protection is performed.
+ */
+ local_irq_save(flags);
+ cpu = raw_smp_processor_id();
+ data = tr->data[cpu];
+ disabled = atomic_inc_return(&data->disabled);
+
+ if (likely(disabled == 1)) {
+ pc = preempt_count();
+ /*
+ * skip over 5 funcs:
+ * __ftrace_trace_stack,
+ * __trace_stack,
+ * function_stack_trace_call
+ * ftrace_list_func
+ * ftrace_call
+ */
+ __trace_stack(tr, data, flags, 5, pc);
+ }
+
+ atomic_dec(&data->disabled);
+ local_irq_restore(flags);
+}
+
+static struct ftrace_ops trace_stack_ops __read_mostly =
+{
+ .func = function_stack_trace_call,
+};
+
+/* Our two options */
+enum {
+ TRACE_FUNC_OPT_STACK = 0x1,
+};
+
+static struct tracer_opt func_opts[] = {
+#ifdef CONFIG_STACKTRACE
+ { TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },
+#endif
+ { } /* Always set a last empty entry */
+};
+
+static struct tracer_flags func_flags = {
+ .val = 0, /* By default: all flags disabled */
+ .opts = func_opts
+};
+
+static int func_set_flag(u32 old_flags, u32 bit, int set)
+{
+ if (bit == TRACE_FUNC_OPT_STACK) {
+ /* do nothing if already set */
+ if (!!set == !!(func_flags.val & TRACE_FUNC_OPT_STACK))
+ return 0;
+
+ if (set)
+ register_ftrace_function(&trace_stack_ops);
+ else
+ unregister_ftrace_function(&trace_stack_ops);
+
+ return 0;
+ }
+
+ return -EINVAL;
+}
+
static struct tracer function_trace __read_mostly =
{
.name = "function",
.init = function_trace_init,
.reset = function_trace_reset,
.start = function_trace_start,
+ .flags = &func_flags,
+ .set_flag = func_set_flag,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_function,
#endif