misc: tegra-throughput: prevent race on init

prevent a race condition on initialization which could result in
multiple notifier registrations.

Bug 1027664

Change-Id: I2e7dcad159f631a7e244d43019169fdaf195bc34
(cherry picked from commit 06ad60cd85a221eec673654c73d55fba34455a3a)
Reviewed-on: http://git-master/r/121143
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Tested-by: Ilan Aelion <iaelion@nvidia.com>
Reviewed-by: Michael I Gold <gold@nvidia.com>

1 files changed, 16 insertions, 6 deletions

diff --git a/drivers/misc/tegra-throughput.c b/drivers/misc/tegra-throughput.c
index 2ab0e516c41c..47dc682795ab 100644
--- a/drivers/misc/tegra-throughput.c
+++ b/drivers/misc/tegra-throughput.c
@@ -99,19 +99,24 @@ static int notifier_initialized;
 
 static int throughput_open(struct inode *inode, struct file *file)
 {
+	int need_init = 0;
+
+	spin_lock(&lock);
+
 	if (!notifier_initialized) {
-		tegra_dc_register_flip_notifier(&throughput_flip_nb);
 		notifier_initialized = 1;
+		need_init = 1;
 	}
 
-	spin_lock(&lock);
-
 	throughput_active_app_count++;
 	if (throughput_active_app_count > 1)
 		multiple_app_disable = 1;
 
 	spin_unlock(&lock);
 
+	if (need_init)
+		tegra_dc_register_flip_notifier(&throughput_flip_nb);
+
 	pr_debug("throughput_open node %p file %p\n", inode, file);
 
 	return 0;
@@ -119,17 +124,22 @@ static int throughput_open(struct inode *inode, struct file *file)
 
 static int throughput_release(struct inode *inode, struct file *file)
 {
+	int need_deinit = 0;
+
 	spin_lock(&lock);
-	throughput_active_app_count--;
-	spin_unlock(&lock);
 
+	throughput_active_app_count--;
 	if (throughput_active_app_count == 0) {
 		reset_target_frame_time();
 		multiple_app_disable = 0;
-		tegra_dc_unregister_flip_notifier(&throughput_flip_nb);
 		notifier_initialized = 0;
+		need_deinit = 1;
 	}
 
+	spin_unlock(&lock);
+
+	if (need_deinit)
+		tegra_dc_unregister_flip_notifier(&throughput_flip_nb);
 
 	pr_debug("throughput_release node %p file %p\n", inode, file);