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>

1 files changed, 17 insertions, 9 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dcb757f70d21..3c54cb125228 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -835,10 +835,10 @@ ftrace(struct trace_array *tr, struct trace_array_cpu *data,
                 trace_function(tr, data, ip, parent_ip, flags, pc);
 }
 
-static void ftrace_trace_stack(struct trace_array *tr,
-                               struct trace_array_cpu *data,
-                               unsigned long flags,
-                               int skip, int pc)
+static void __ftrace_trace_stack(struct trace_array *tr,
+                                 struct trace_array_cpu *data,
+                                 unsigned long flags,
+                                 int skip, int pc)
 {
 #ifdef CONFIG_STACKTRACE
         struct ring_buffer_event *event;
@@ -846,9 +846,6 @@ static void ftrace_trace_stack(struct trace_array *tr,
         struct stack_trace trace;
         unsigned long irq_flags;
 
-        if (!(trace_flags & TRACE_ITER_STACKTRACE))
-                return;
-
         event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry),
                                          &irq_flags);
         if (!event)
@@ -869,12 +866,23 @@ static void ftrace_trace_stack(struct trace_array *tr,
 #endif
 }
 
+static void ftrace_trace_stack(struct trace_array *tr,
+                               struct trace_array_cpu *data,
+                               unsigned long flags,
+                               int skip, int pc)
+{
+        if (!(trace_flags & TRACE_ITER_STACKTRACE))
+                return;
+
+        __ftrace_trace_stack(tr, data, flags, skip, pc);
+}
+
 void __trace_stack(struct trace_array *tr,
                    struct trace_array_cpu *data,
                    unsigned long flags,
-                   int skip)
+                   int skip, int pc)
 {
-        ftrace_trace_stack(tr, data, flags, skip, preempt_count());
+        __ftrace_trace_stack(tr, data, flags, skip, pc);
 }
 
 static void ftrace_trace_userstack(struct trace_array *tr,