tracing/filter: Remove empty subsystem and its directory

Remove empty subsystem and its directory when module unload.

Before patch:
 # rmmod trace-events-sample.ko
 # ls sample
 enable  filter

After patch:
 # rmmod trace-events-sample.ko
 # ls sample
 ls: cannot access sample: No such file or directory

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Acked-by: Tom Zanussi <tzanussi@gmail.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A55A8BE.9010707@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 32 insertions, 1 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 52eb0d8dcd75..94305c7bc11c 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -757,6 +757,7 @@ struct event_subsystem {
         const char              *name;
         struct dentry           *entry;
         void                    *filter;
+        int                     nr_events;
 };
 
 struct filter_pred;
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index fecac1314cbe..90cf9360e140 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -851,8 +851,10 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
 
         /* First see if we did not already create this dir */
         list_for_each_entry(system, &event_subsystems, list) {
-                if (strcmp(system->name, name) == 0)
+                if (strcmp(system->name, name) == 0) {
+                        system->nr_events++;
                         return system->entry;
+                }
         }
 
         /* need to create new entry */
@@ -871,6 +873,7 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
                 return d_events;
         }
 
+        system->nr_events = 1;
         system->name = kstrdup(name, GFP_KERNEL);
         if (!system->name) {
                 debugfs_remove(system->entry);
@@ -905,6 +908,32 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
         return system->entry;
 }
 
+static void remove_subsystem_dir(const char *name)
+{
+        struct event_subsystem *system;
+
+        if (strcmp(name, TRACE_SYSTEM) == 0)
+                return;
+
+        list_for_each_entry(system, &event_subsystems, list) {
+                if (strcmp(system->name, name) == 0) {
+                        if (!--system->nr_events) {
+                                struct event_filter *filter = system->filter;
+
+                                debugfs_remove_recursive(system->entry);
+                                list_del(&system->list);
+                                if (filter) {
+                                        kfree(filter->filter_string);
+                                        kfree(filter);
+                                }
+                                kfree(system->name);
+                                kfree(system);
+                        }
+                        break;
+                }
+        }
+}
+
 static int
 event_create_dir(struct ftrace_event_call *call, struct dentry *d_events,
                  const struct file_operations *id,
@@ -1079,6 +1108,7 @@ static void trace_module_remove_events(struct module *mod)
                         list_del(&call->list);
                         trace_destroy_fields(call);
                         destroy_preds(call);
+                        remove_subsystem_dir(call->system);
                 }
         }