tracing/ftrace: Add a better way to pass data via the probe functions

With the redesign of the registration and execution of the function probes
(triggers), data can now be passed from the setup of the probe to the probe
callers that are specific to the trace_array it is on. Although, all probes
still only affect the toplevel trace array, this change will allow for
instances to have their own probes separated from other instances and the
top array.

That is, something like the stacktrace probe can be set to trace only in an
instance and not the toplevel trace array. This isn't implement yet, but
this change sets the ground work for the change.

When a probe callback is triggered (someone writes the probe format into
set_ftrace_filter), it calls register_ftrace_function_probe() passing in
init_data that will be used to initialize the probe. Then for every matching
function, register_ftrace_function_probe() will call the probe_ops->init()
function with the init data that was passed to it, as well as an address to
a place holder that is associated with the probe and the instance. The first
occurrence will have a NULL in the pointer. The init() function will then
initialize it. If other probes are added, or more functions are part of the
probe, the place holder will be passed to the init() function with the place
holder data that it was initialized to the last time.

Then this place_holder is passed to each of the other probe_ops functions,
where it can be used in the function callback. When the probe_ops free()
function is called, it can be called either with the rip of the function
that is being removed from the probe, or zero, indicating that there are no
more functions attached to the probe, and the place holder is about to be
freed. This gives the probe_ops a way to free the data it assigned to the
place holder if it was allocade during the first init call.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 23 insertions, 15 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e61610e5e6e3..18256cd7ad2c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6737,7 +6737,7 @@ static const struct file_operations tracing_dyn_info_fops = {
 static void
 ftrace_snapshot(unsigned long ip, unsigned long parent_ip,
                 struct trace_array *tr, struct ftrace_probe_ops *ops,
-                void **data)
+                void *data)
 {
         tracing_snapshot();
 }
@@ -6745,9 +6745,9 @@ ftrace_snapshot(unsigned long ip, unsigned long parent_ip,
 static void
 ftrace_count_snapshot(unsigned long ip, unsigned long parent_ip,
                       struct trace_array *tr, struct ftrace_probe_ops *ops,
-                      void **data)
+                      void *data)
 {
-        struct ftrace_func_mapper *mapper = ops->private_data;
+        struct ftrace_func_mapper *mapper = data;
         long *count = NULL;
 
         if (mapper)
@@ -6768,7 +6768,7 @@ static int
 ftrace_snapshot_print(struct seq_file *m, unsigned long ip,
                       struct ftrace_probe_ops *ops, void *data)
 {
-        struct ftrace_func_mapper *mapper = ops->private_data;
+        struct ftrace_func_mapper *mapper = data;
         long *count = NULL;
 
         seq_printf(m, "%ps:", (void *)ip);
@@ -6788,18 +6788,32 @@ ftrace_snapshot_print(struct seq_file *m, unsigned long ip,
 
 static int
 ftrace_snapshot_init(struct ftrace_probe_ops *ops, struct trace_array *tr,
-                     unsigned long ip, void *data)
+                     unsigned long ip, void *init_data, void **data)
 {
-        struct ftrace_func_mapper *mapper = ops->private_data;
+        struct ftrace_func_mapper *mapper = *data;
+
+        if (!mapper) {
+                mapper = allocate_ftrace_func_mapper();
+                if (!mapper)
+                        return -ENOMEM;
+                *data = mapper;
+        }
 
-        return ftrace_func_mapper_add_ip(mapper, ip, data);
+        return ftrace_func_mapper_add_ip(mapper, ip, init_data);
 }
 
 static void
 ftrace_snapshot_free(struct ftrace_probe_ops *ops, struct trace_array *tr,
-                     unsigned long ip, void **data)
+                     unsigned long ip, void *data)
 {
-        struct ftrace_func_mapper *mapper = ops->private_data;
+        struct ftrace_func_mapper *mapper = data;
+
+        if (!ip) {
+                if (!mapper)
+                        return;
+                free_ftrace_func_mapper(mapper, NULL);
+                return;
+        }
 
         ftrace_func_mapper_remove_ip(mapper, ip);
 }
@@ -6842,12 +6856,6 @@ ftrace_trace_snapshot_callback(struct trace_array *tr, struct ftrace_hash *hash,
         if (!strlen(number))
                 goto out_reg;
 
-        if (!ops->private_data) {
-                ops->private_data = allocate_ftrace_func_mapper();
-                if (!ops->private_data)
-                        return -ENOMEM;
-        }
-
         /*
          * We use the callback data field (which is a pointer)
          * as our counter.