msm: kgsl: Avoid racing against context delete while releasing contexts

While releasing contexts take a reference to context inside read rcu
lock to avoid racing against context deletion. This will avoid using
dangling context pointer in device_release_contexts.

Change-Id: I76e787f6dde5a324fec23e81829174bd28134c6c
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>

1 files changed, 11 insertions, 8 deletions

diff --git a/drivers/gpu/msm/kgsl.c b/drivers/gpu/msm/kgsl.c
index 8a8e19cf9f6d..841e7e450baa 100644
--- a/drivers/gpu/msm/kgsl.c
+++ b/drivers/gpu/msm/kgsl.c
@@ -1071,25 +1071,28 @@ static void device_release_contexts(struct kgsl_device_private *dev_priv)
 	struct kgsl_device *device = dev_priv->device;
 	struct kgsl_context *context;
 	int next = 0;
+	int result = 0;
 
 	while (1) {
 		read_lock(&device->context_lock);
 		context = idr_get_next(&device->context_idr, &next);
-		read_unlock(&device->context_lock);
 
-		if (context == NULL)
+		if (context == NULL) {
+			read_unlock(&device->context_lock);
 			break;
-
-		if (context->dev_priv == dev_priv) {
+		} else if (context->dev_priv == dev_priv) {
 			/*
 			 * Hold a reference to the context in case somebody
 			 * tries to put it while we are detaching
 			 */
+			result = _kgsl_context_get(context);
+		}
+		read_unlock(&device->context_lock);
 
-			if (_kgsl_context_get(context)) {
-				kgsl_context_detach(context);
-				kgsl_context_put(context);
-			}
+		if (result) {
+			kgsl_context_detach(context);
+			kgsl_context_put(context);
+			result = 0;
 		}
 
 		next = next + 1;