tracing: let user specify tracing_thresh after selecting function_graph

Currently, tracing_thresh works only if we specify it before selecting
function_graph tracer. If we do the opposite, tracing_thresh will change
it's value, but it will not be applied.
To fix it, we add update_thresh callback which is called whenever
tracing_thresh is updated and for function_graph tracer we register
handler which reinitializes tracer depending on tracing_thresh.

Link: http://lkml.kernel.org/p/20140718111727.GA3206@stfomichev-desktop.yandex.net

Signed-off-by: Stanislav Fomichev <stfomichev@yandex-team.ru>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 67 insertions, 7 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4a343db45d4e..2752147ed317 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4201,10 +4201,9 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
 }
 
 static ssize_t
-tracing_max_lat_read(struct file *filp, char __user *ubuf,
-                     size_t cnt, loff_t *ppos)
+tracing_nsecs_read(unsigned long *ptr, char __user *ubuf,
+                   size_t cnt, loff_t *ppos)
 {
-        unsigned long *ptr = filp->private_data;
         char buf[64];
         int r;
 
@@ -4216,10 +4215,9 @@ tracing_max_lat_read(struct file *filp, char __user *ubuf,
 }
 
 static ssize_t
-tracing_max_lat_write(struct file *filp, const char __user *ubuf,
-                      size_t cnt, loff_t *ppos)
+tracing_nsecs_write(unsigned long *ptr, const char __user *ubuf,
+                    size_t cnt, loff_t *ppos)
 {
-        unsigned long *ptr = filp->private_data;
         unsigned long val;
         int ret;
 
@@ -4232,6 +4230,52 @@ tracing_max_lat_write(struct file *filp, const char __user *ubuf,
         return cnt;
 }
 
+static ssize_t
+tracing_thresh_read(struct file *filp, char __user *ubuf,
+                    size_t cnt, loff_t *ppos)
+{
+        return tracing_nsecs_read(&tracing_thresh, ubuf, cnt, ppos);
+}
+
+static ssize_t
+tracing_thresh_write(struct file *filp, const char __user *ubuf,
+                     size_t cnt, loff_t *ppos)
+{
+        struct trace_array *tr = filp->private_data;
+        int ret;
+
+        mutex_lock(&trace_types_lock);
+        ret = tracing_nsecs_write(&tracing_thresh, ubuf, cnt, ppos);
+        if (ret < 0)
+                goto out;
+
+        if (tr->current_trace->update_thresh) {
+                ret = tr->current_trace->update_thresh(tr);
+                if (ret < 0)
+                        goto out;
+        }
+
+        ret = cnt;
+out:
+        mutex_unlock(&trace_types_lock);
+
+        return ret;
+}
+
+static ssize_t
+tracing_max_lat_read(struct file *filp, char __user *ubuf,
+                     size_t cnt, loff_t *ppos)
+{
+        return tracing_nsecs_read(filp->private_data, ubuf, cnt, ppos);
+}
+
+static ssize_t
+tracing_max_lat_write(struct file *filp, const char __user *ubuf,
+                      size_t cnt, loff_t *ppos)
+{
+        return tracing_nsecs_write(filp->private_data, ubuf, cnt, ppos);
+}
+
 static int tracing_open_pipe(struct inode *inode, struct file *filp)
 {
         struct trace_array *tr = inode->i_private;
@@ -5133,6 +5177,13 @@ static int snapshot_raw_open(struct inode *inode, struct file *filp)
 #endif /* CONFIG_TRACER_SNAPSHOT */
 
 
+static const struct file_operations tracing_thresh_fops = {
+        .open           = tracing_open_generic,
+        .read           = tracing_thresh_read,
+        .write          = tracing_thresh_write,
+        .llseek         = generic_file_llseek,
+};
+
 static const struct file_operations tracing_max_lat_fops = {
         .open           = tracing_open_generic,
         .read           = tracing_max_lat_read,
@@ -6494,7 +6545,7 @@ static __init int tracer_init_debugfs(void)
         init_tracer_debugfs(&global_trace, d_tracer);
 
         trace_create_file("tracing_thresh", 0644, d_tracer,
-                        &tracing_thresh, &tracing_max_lat_fops);
+                        &global_trace, &tracing_thresh_fops);
 
         trace_create_file("README", 0444, d_tracer,
                         NULL, &tracing_readme_fops);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 9258f5a815db..385391fb1d3b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -339,6 +339,7 @@ struct tracer_flags {
  * @reset: called when one switches to another tracer
  * @start: called when tracing is unpaused (echo 1 > tracing_enabled)
  * @stop: called when tracing is paused (echo 0 > tracing_enabled)
+ * @update_thresh: called when tracing_thresh is updated
  * @open: called when the trace file is opened
  * @pipe_open: called when the trace_pipe file is opened
  * @close: called when the trace file is released
@@ -357,6 +358,7 @@ struct tracer {
         void                    (*reset)(struct trace_array *tr);
         void                    (*start)(struct trace_array *tr);
         void                    (*stop)(struct trace_array *tr);
+        int                     (*update_thresh)(struct trace_array *tr);
         void                    (*open)(struct trace_iterator *iter);
         void                    (*pipe_open)(struct trace_iterator *iter);
         void                    (*close)(struct trace_iterator *iter);
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 2c944e6c4a9d..74d98820497c 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -475,6 +475,12 @@ static void graph_trace_reset(struct trace_array *tr)
         unregister_ftrace_graph();
 }
 
+int graph_trace_update_thresh(struct trace_array *tr)
+{
+        graph_trace_reset(tr);
+        return graph_trace_init(tr);
+}
+
 static int max_bytes_for_cpu;
 
 static enum print_line_t
@@ -1525,6 +1531,7 @@ static struct trace_event graph_trace_ret_event = {
 
 static struct tracer graph_trace __tracer_data = {
         .name           = "function_graph",
+        .update_thresh  = graph_trace_update_thresh,
         .open           = graph_trace_open,
         .pipe_open      = graph_trace_open,
         .close          = graph_trace_close,