dma-buf: remove restriction of IOCTL:DMA_BUF_SET_NAME

In this patch(https://patchwork.freedesktop.org/patch/310349),
it add a new IOCTL to support dma-buf user to set debug name.

But it also added a limitation of this IOCTL, it needs the
attachments of dmabuf should be empty, otherwise it will fail.

For the original series, the idea was that allowing name change
mid-use could confuse the users about the dma-buf.
However, the rest of the series also makes sure each dma-buf have a unique
inode(https://patchwork.freedesktop.org/patch/310387/), and any accounting
should probably use that, without relying on the name as much.

So, removing this restriction will let dma-buf userspace users to use it
more comfortably and without any side effect.
Signed-off-by: Guangming Cao <Guangming.Cao@mediatek.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211014102551.54983-1-guangming.cao@mediatek.comReviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/dma-buf/dma-buf.c

@@ -293,10 +293,8 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 
 /**
  * dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
- * The name of the dma-buf buffer can only be set when the dma-buf is not
- * attached to any devices. It could theoritically support changing the
- * name of the dma-buf if the same piece of memory is used for multiple
- * purpose between different devices.
+ * It could support changing the name of the dma-buf if the same
+ * piece of memory is used for multiple purpose between different devices.
  *
  * @dmabuf: [in]     dmabuf buffer that will be renamed.
  * @buf:    [in]     A piece of userspace memory that contains the name of
@@ -309,25 +307,16 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
 {
 	char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
-	long ret = 0;
 
 	if (IS_ERR(name))
 		return PTR_ERR(name);
 
-	dma_resv_lock(dmabuf->resv, NULL);
-	if (!list_empty(&dmabuf->attachments)) {
-		ret = -EBUSY;
-		kfree(name);
-		goto out_unlock;
-	}
 	spin_lock(&dmabuf->name_lock);
 	kfree(dmabuf->name);
 	dmabuf->name = name;
 	spin_unlock(&dmabuf->name_lock);
 
-out_unlock:
-	dma_resv_unlock(dmabuf->resv);
-	return ret;
+	return 0;
 }
 
 static long dma_buf_ioctl(struct file *file,