tracing: Fix bug when reading system filters on module removal

[linux-imx.git] / kernel / trace / trace_events.c

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 686ec399f2a83a007ddacfdbd07fd7cced24783f..ffc5b2884af14a1297cfc090e0f5793533c221b9 100644 (file)
--- 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;
                }