vhost: don't hold onto file pointer for VHOST_SET_LOG_FD

We already hold a reference to the eventfd_ctx, which is sufficient;
there's no need to hold a reference to the struct file as well.  So get
rid of vhost_dev->log_file.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>

drivers/vhost/vhost.c

@@ -419,7 +419,6 @@ void vhost_dev_init(struct vhost_dev *dev,
 	dev->nvqs = nvqs;
 	mutex_init(&dev->mutex);
 	dev->log_ctx = NULL;
-	dev->log_file = NULL;
 	dev->umem = NULL;
 	dev->iotlb = NULL;
 	dev->mm = NULL;
@@ -625,9 +624,6 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
 	if (dev->log_ctx)
 		eventfd_ctx_put(dev->log_ctx);
 	dev->log_ctx = NULL;
-	if (dev->log_file)
-		fput(dev->log_file);
-	dev->log_file = NULL;
 	/* No one will access memory at this point */
 	vhost_umem_clean(dev->umem);
 	dev->umem = NULL;
@@ -1572,8 +1568,7 @@ EXPORT_SYMBOL_GPL(vhost_init_device_iotlb);
 /* Caller must have device mutex */
 long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 {
-	struct file *eventfp, *filep = NULL;
-	struct eventfd_ctx *ctx = NULL;
+	struct eventfd_ctx *ctx;
 	u64 p;
 	long r;
 	int i, fd;
@@ -1619,19 +1614,12 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 		r = get_user(fd, (int __user *)argp);
 		if (r < 0)
 			break;
-		eventfp = fd == -1 ? NULL : eventfd_fget(fd);
-		if (IS_ERR(eventfp)) {
-			r = PTR_ERR(eventfp);
+		ctx = fd == -1 ? NULL : eventfd_ctx_fdget(fd);
+		if (IS_ERR(ctx)) {
+			r = PTR_ERR(ctx);
 			break;
 		}
-		if (eventfp != d->log_file) {
-			filep = d->log_file;
-			d->log_file = eventfp;
-			ctx = d->log_ctx;
-			d->log_ctx = eventfp ?
-				eventfd_ctx_fileget(eventfp) : NULL;
-		} else
-			filep = eventfp;
+		swap(ctx, d->log_ctx);
 		for (i = 0; i < d->nvqs; ++i) {
 			mutex_lock(&d->vqs[i]->mutex);
 			d->vqs[i]->log_ctx = d->log_ctx;
@@ -1639,8 +1627,6 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 		}
 		if (ctx)
 			eventfd_ctx_put(ctx);
-		if (filep)
-			fput(filep);
 		break;
 	default:
 		r = -ENOIOCTLCMD;

drivers/vhost/vhost.h

@@ -157,7 +157,6 @@ struct vhost_dev {
 	struct mutex mutex;
 	struct vhost_virtqueue **vqs;
 	int nvqs;
-	struct file *log_file;
 	struct eventfd_ctx *log_ctx;
 	struct llist_head work_list;
 	struct task_struct *worker;