Feather-Trace device interface: synchronize event activation/deactivation

The platform code does not synchronize anything, so make sure there's
only one caller at any time.

1 files changed, 7 insertions, 0 deletions

diff --git a/litmus/ftdev.c b/litmus/ftdev.c
index 095301a23450..646e8c9fe230 100644
--- a/litmus/ftdev.c
+++ b/litmus/ftdev.c
@@ -6,6 +6,7 @@
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/vmalloc.h>
+#include <linux/mutex.h>
 
 #include <litmus/feather_trace.h>
 #include <litmus/ftdev.h>
@@ -51,13 +52,17 @@ struct ftdev_event {
         struct ftdev_event* next;
 };
 
+static DEFINE_MUTEX(ft_event_activation_mutex);
+
 static int activate(struct ftdev_event** chain, int id)
 {
         struct ftdev_event* ev = kmalloc(sizeof(*ev), GFP_KERNEL);
         if (ev) {
+                mutex_lock(&ft_event_activation_mutex);
                 printk(KERN_INFO
                        "Enabling feather-trace event %d.\n", (int) id);
                 ft_enable_event(id);
+                mutex_unlock(&ft_event_activation_mutex);
                 ev->id = id;
                 ev->next = *chain;
                 *chain    = ev;
@@ -76,7 +81,9 @@ static void deactivate(struct ftdev_event** chain, int id)
                         *cur  = nxt;
                         printk(KERN_INFO
                                "Disabling feather-trace event %d.\n", (int) id);
+                        mutex_lock(&ft_event_activation_mutex);
                         ft_disable_event(id);
+                        mutex_unlock(&ft_event_activation_mutex);
                         break;
                 }
                 cur = &(*cur)->next;