3 files changed, 82 insertions, 11 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 229f8591f61d..f8074072d111 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -677,6 +677,7 @@ struct event_subsystem {
         struct dentry           *entry;
         struct event_filter     *filter;
         int                     nr_events;
+        int                     ref_count;
 };
 
 #define FILTER_PRED_INVALID     ((unsigned short)-1)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 686ec399f2a8..ffc5b2884af1 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -244,6 +244,35 @@ static void ftrace_clear_events(void)
         mutex_unlock(&event_mutex);
 }
 
+static void __put_system(struct event_subsystem *system)
+{
+        struct event_filter *filter = system->filter;
+
+        WARN_ON_ONCE(system->ref_count == 0);
+        if (--system->ref_count)
+                return;
+
+        if (filter) {
+                kfree(filter->filter_string);
+                kfree(filter);
+        }
+        kfree(system->name);
+        kfree(system);
+}
+
+static void __get_system(struct event_subsystem *system)
+{
+        WARN_ON_ONCE(system->ref_count == 0);
+        system->ref_count++;
+}
+
+static void put_system(struct event_subsystem *system)
+{
+        mutex_lock(&event_mutex);
+        __put_system(system);
+        mutex_unlock(&event_mutex);
+}
+
 /*
  * __ftrace_set_clr_event(NULL, NULL, NULL, set) will set/unset all events.
  */
@@ -826,6 +855,47 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
         return cnt;
 }
 
+static LIST_HEAD(event_subsystems);
+
+static int subsystem_open(struct inode *inode, struct file *filp)
+{
+        struct event_subsystem *system = NULL;
+        int ret;
+
+        /* Make sure the system still exists */
+        mutex_lock(&event_mutex);
+        list_for_each_entry(system, &event_subsystems, list) {
+                if (system == inode->i_private) {
+                        /* Don't open systems with no events */
+                        if (!system->nr_events) {
+                                system = NULL;
+                                break;
+                        }
+                        __get_system(system);
+                        break;
+                }
+        }
+        mutex_unlock(&event_mutex);
+
+        if (system != inode->i_private)
+                return -ENODEV;
+
+        ret = tracing_open_generic(inode, filp);
+        if (ret < 0)
+                put_system(system);
+
+        return ret;
+}
+
+static int subsystem_release(struct inode *inode, struct file *file)
+{
+        struct event_subsystem *system = inode->i_private;
+
+        put_system(system);
+
+        return 0;
+}
+
 static ssize_t
 subsystem_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
                       loff_t *ppos)
@@ -963,10 +1033,11 @@ static const struct file_operations ftrace_event_filter_fops = {
 };
 
 static const struct file_operations ftrace_subsystem_filter_fops = {
-        .open = tracing_open_generic,
+        .open = subsystem_open,
         .read = subsystem_filter_read,
         .write = subsystem_filter_write,
         .llseek = default_llseek,
+        .release = subsystem_release,
 };
 
 static const struct file_operations ftrace_system_enable_fops = {
@@ -1002,8 +1073,6 @@ static struct dentry *event_trace_events_dir(void)
         return d_events;
 }
 
-static LIST_HEAD(event_subsystems);
-
 static struct dentry *
 event_subsystem_dir(const char *name, struct dentry *d_events)
 {
@@ -1013,6 +1082,7 @@ 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) {
+                        __get_system(system);
                         system->nr_events++;
                         return system->entry;
                 }
@@ -1035,6 +1105,7 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
         }
 
         system->nr_events = 1;
+        system->ref_count = 1;
         system->name = kstrdup(name, GFP_KERNEL);
         if (!system->name) {
                 debugfs_remove(system->entry);
@@ -1184,16 +1255,9 @@ static void remove_subsystem_dir(const char *name)
         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);
+                                __put_system(system);
                         }
                         break;
                 }
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 8008ddcfbf20..256764ecccd6 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1886,6 +1886,12 @@ int apply_subsystem_event_filter(struct event_subsystem *system,
 
         mutex_lock(&event_mutex);
 
+        /* Make sure the system still has events */
+        if (!system->nr_events) {
+                err = -ENODEV;
+                goto out_unlock;
+        }
+
         if (!strcmp(strstrip(filter_string), "0")) {
                 filter_free_subsystem_preds(system);
                 remove_filter_string(system->filter);