tracing: Add rmdir to remove multibuffer instances

Add a method to the hijacked dentry descriptor of the
"instances" directory to allow for rmdir to remove an
instance of a multibuffer.

Example:

  cd /debug/tracing/instances
  mkdir hello
  ls
hello/
  rmdir hello
  ls

Like the mkdir method, the i_mutex is dropped for the instances
directory. The instances directory is created at boot up and can
not be renamed or removed. The trace_types_lock mutex is used to
synchronize adding and removing of instances.

I've run several stress tests with different threads trying to
create and delete directories of the same name, and it has stood
up fine.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 58a61302a733..06d6bc275221 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1709,6 +1709,20 @@ __trace_add_event_dirs(struct trace_array *tr)
         }
 }
 
+/* Remove the event directory structure for a trace directory. */
+static void
+__trace_remove_event_dirs(struct trace_array *tr)
+{
+        struct ftrace_event_file *file, *next;
+
+        list_for_each_entry_safe(file, next, &tr->events, list) {
+                list_del(&file->list);
+                debugfs_remove_recursive(file->dir);
+                remove_subsystem(file->system);
+                kfree(file);
+        }
+}
+
 static void
 __add_event_to_tracers(struct ftrace_event_call *call,
                        struct ftrace_module_file_ops *file_ops)
@@ -1793,6 +1807,25 @@ int event_trace_add_tracer(struct dentry *parent, struct trace_array *tr)
         return 0;
 }
 
+int event_trace_del_tracer(struct trace_array *tr)
+{
+        /* Disable any running events */
+        __ftrace_set_clr_event(tr, NULL, NULL, NULL, 0);
+
+        mutex_lock(&event_mutex);
+
+        down_write(&trace_event_mutex);
+        __trace_remove_event_dirs(tr);
+        debugfs_remove_recursive(tr->event_dir);
+        up_write(&trace_event_mutex);
+
+        tr->event_dir = NULL;
+
+        mutex_unlock(&event_mutex);
+
+        return 0;
+}
+
 static __init int event_trace_enable(void)
 {
         struct trace_array *tr = top_trace_array();