sync_file: Return consistent status in SYNC_IOC_FILE_INFO

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 <[e-mail]>
Signed-off-by: John Einar Reitan <[e-mail]>
Cc: Sumit Semwal <[e-mail]>
Cc: Gustavo Padovan <[e-mail]>
Cc: [e-mail]
Reviewed-by: Chris Wilson <[e-mail]>
Signed-off-by: Gustavo Padovan <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/dma-buf/sync_file.c

···
 	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),
···
 		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,
···
 	 * sync_fence_info and return the actual number of fences on
 	 * info->num_fences.
 	 */
-	if (!info.num_fences)
+	if (!info.num_fences) {
+		info.status = dma_fence_is_signaled(sync_file->fence);
 		goto no_fences;
+	} else {
+		info.status = 1;
+	}
 
 	if (info.num_fences < num_fences)
 		return -EINVAL;
···
 	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]);
+		info.status = info.status <= 0 ? info.status : status;
+	}
 
 	if (copy_to_user(u64_to_user_ptr(info.sync_fence_info), fence_info,
 			 size)) {
···
 
 no_fences:
 	sync_file_get_name(sync_file, info.name, sizeof(info.name));
-	info.status = dma_fence_is_signaled(sync_file->fence);
 	info.num_fences = num_fences;
 
 	if (copy_to_user((void __user *)arg, &info, sizeof(info)))