tracing: Clear all trace buffers when unloaded module event was used

Currently we do not know what buffer a module event was enabled in.
On unload, it is safest to clear all buffer instances, not just the
top level buffer.

Todo: Clear only the buffer that the event was used in. The
infrastructure is there to do this, but it makes the code a bit
more complex. Lets get the current code vetted before we add that.

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

3 files changed, 16 insertions, 6 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b5b25b6575a9..c8a852a55db4 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -912,9 +912,15 @@ void tracing_reset_current(int cpu)
         tracing_reset(&global_trace, cpu);
 }
 
-void tracing_reset_current_online_cpus(void)
+void tracing_reset_all_online_cpus(void)
 {
-        tracing_reset_online_cpus(&global_trace);
+        struct trace_array *tr;
+
+        mutex_lock(&trace_types_lock);
+        list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+                tracing_reset_online_cpus(tr);
+        }
+        mutex_unlock(&trace_types_lock);
 }
 
 #define SAVED_CMDLINES 128
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 6728a249e817..fa60b2977524 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -496,7 +496,7 @@ int tracing_is_enabled(void);
 void tracing_reset(struct trace_array *tr, int cpu);
 void tracing_reset_online_cpus(struct trace_array *tr);
 void tracing_reset_current(int cpu);
-void tracing_reset_current_online_cpus(void);
+void tracing_reset_all_online_cpus(void);
 int tracing_open_generic(struct inode *inode, struct file *filp);
 struct dentry *trace_create_file(const char *name,
                                  umode_t mode,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 9a7dc4bf1171..a376ab5eec5c 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1649,14 +1649,18 @@ static void trace_module_remove_events(struct module *mod)
                 list_del(&file_ops->list);
                 kfree(file_ops);
         }
+        up_write(&trace_event_mutex);
 
         /*
          * It is safest to reset the ring buffer if the module being unloaded
-         * registered any events that were used.
+         * registered any events that were used. The only worry is if
+         * a new module gets loaded, and takes on the same id as the events
+         * of this module. When printing out the buffer, traced events left
+         * over from this module may be passed to the new module events and
+         * unexpected results may occur.
          */
         if (clear_trace)
-                tracing_reset_current_online_cpus();
-        up_write(&trace_event_mutex);
+                tracing_reset_all_online_cpus();
 }
 
 static int trace_module_notify(struct notifier_block *self,