[PATCH] sync_file: Return consistent status in SYNC_IOC_FILE_INFO

[John Einar Reitan]

sync_file_ioctl_fence_info has a race between filling the status
of the underlying fences and the overall status of the sync_file.
If fence transitions in the time frame between its sync_fill_fence_info
and the later dma_fence_is_signaled for the sync_file, the returned
information is inconsistent showing non-signaled underlying fences but
an overall signaled state.

This patch changes sync_file_ioctl_fence_info to track what has been
encoded and using that as the overall sync_file status.

Tested-by: Vamsidhar Reddy Gaddam <vamsidhar.gaddam at arm.com>
Signed-off-by: John Einar Reitan <john.reitan at arm.com>
---
 drivers/dma-buf/sync_file.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 66fb40d0ebdb..ebf5764b868c 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -383,7 +383,7 @@ static long sync_file_ioctl_merge(struct sync_file *sync_file,
 	return err;
 }
 
-static void sync_fill_fence_info(struct dma_fence *fence,
+static int sync_fill_fence_info(struct dma_fence *fence,
 				 struct sync_fence_info *info)
 {
 	strlcpy(info->obj_name, fence->ops->get_timeline_name(fence),
@@ -399,6 +399,8 @@ static void sync_fill_fence_info(struct dma_fence *fence,
 		test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags) ?
 		ktime_to_ns(fence->timestamp) :
 		ktime_set(0, 0);
+
+	return info->status;
 }
 
 static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
@@ -408,7 +410,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	struct sync_fence_info *fence_info = NULL;
 	struct dma_fence **fences;
 	__u32 size;
-	int num_fences, ret, i;
+	int num_fences, ret, i, fences_status = 1;
 
 	if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
 		return -EFAULT;
@@ -424,8 +426,10 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	 * sync_fence_info and return the actual number of fences on
 	 * info->num_fences.
 	 */
-	if (!info.num_fences)
+	if (!info.num_fences) {
+		fences_status = dma_fence_is_signaled(sync_file->fence);
 		goto no_fences;
+	}
 
 	if (info.num_fences < num_fences)
 		return -EINVAL;
@@ -435,8 +439,10 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (!fence_info)
 		return -ENOMEM;
 
-	for (i = 0; i < num_fences; i++)
-		sync_fill_fence_info(fences[i], &fence_info[i]);
+	for (i = 0; i < num_fences; i++) {
+		int status = sync_fill_fence_info(fences[i], &fence_info[i]);
+		fences_status = fences_status <= 0 ? fences_status : status;
+	}
 
 	if (copy_to_user(u64_to_user_ptr(info.sync_fence_info), fence_info,
 			 size)) {
@@ -446,7 +452,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 
 no_fences:
 	sync_file_get_name(sync_file, info.name, sizeof(info.name));
-	info.status = dma_fence_is_signaled(sync_file->fence);
+	info.status = fences_status;
 	info.num_fences = num_fences;
 
 	if (copy_to_user((void __user *)arg, &info, sizeof(info)))
-- 
2.13.6