[PATCH v6 1/4] sync_file: Protect access to driver and timeline name

[Tvrtko Ursulin]

Protect the access to driver and timeline name which otherwise could be
freed as dma-fence exported is signalling fences.

This prepares the code for incoming dma-fence API changes which will start
asserting these accesses are done from a RCU locked section.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
---
 drivers/dma-buf/sync_file.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 212df4b849fe..747e377fb954 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -135,12 +135,18 @@ char *sync_file_get_name(struct sync_file *sync_file, char *buf, int len)
 		strscpy(buf, sync_file->user_name, len);
 	} else {
 		struct dma_fence *fence = sync_file->fence;
+		const char __rcu *timeline;
+		const char __rcu *driver;
 
+		rcu_read_lock();
+		driver = dma_fence_driver_name(fence);
+		timeline = dma_fence_timeline_name(fence);
 		snprintf(buf, len, "%s-%s%llu-%lld",
-			 dma_fence_driver_name(fence),
-			 dma_fence_timeline_name(fence),
+			 rcu_dereference(driver),
+			 rcu_dereference(timeline),
 			 fence->context,
 			 fence->seqno);
+		rcu_read_unlock();
 	}
 
 	return buf;
@@ -262,9 +268,17 @@ static long sync_file_ioctl_merge(struct sync_file *sync_file,
 static int sync_fill_fence_info(struct dma_fence *fence,
 				 struct sync_fence_info *info)
 {
-	strscpy(info->obj_name, dma_fence_timeline_name(fence),
+	const char __rcu *timeline;
+	const char __rcu *driver;
+
+	rcu_read_lock();
+
+	driver = dma_fence_driver_name(fence);
+	timeline = dma_fence_timeline_name(fence);
+
+	strscpy(info->obj_name, rcu_dereference(timeline),
 		sizeof(info->obj_name));
-	strscpy(info->driver_name, dma_fence_driver_name(fence),
+	strscpy(info->driver_name, rcu_dereference(driver),
 		sizeof(info->driver_name));
 
 	info->status = dma_fence_get_status(fence);
@@ -273,6 +287,8 @@ static int sync_fill_fence_info(struct dma_fence *fence,
 			ktime_to_ns(dma_fence_timestamp(fence)) :
 			ktime_set(0, 0);
 
+	rcu_read_unlock();
+
 	return info->status;
 }
 
-- 
2.48.0