media: videobuf2: Fix IS_ERR checking in vb2_vmalloc_put_userptr()

In order to avoid error pointers from frame_vector_pages(), we could
use IS_ERR() to check the return value to fix this. This checking
operation could make sure that vector contains pages.
Signed-off-by: Ma Ke <make_ruc2021@163.com>
Acked-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil: add space between ){]
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/common/videobuf2/videobuf2-vmalloc.c

@@ -133,13 +133,15 @@ static void vb2_vmalloc_put_userptr(void *buf_priv)
 
 	if (!buf->vec->is_pfns) {
 		n_pages = frame_vector_count(buf->vec);
-		pages = frame_vector_pages(buf->vec);
 		if (vaddr)
 			vm_unmap_ram((void *)vaddr, n_pages);
 		if (buf->dma_dir == DMA_FROM_DEVICE ||
-		    buf->dma_dir == DMA_BIDIRECTIONAL)
-			for (i = 0; i < n_pages; i++)
-				set_page_dirty_lock(pages[i]);
+		    buf->dma_dir == DMA_BIDIRECTIONAL) {
+			pages = frame_vector_pages(buf->vec);
+			if (!WARN_ON_ONCE(IS_ERR(pages)))
+				for (i = 0; i < n_pages; i++)
+					set_page_dirty_lock(pages[i]);
+		}
 	} else {
 		iounmap((__force void __iomem *)buf->vaddr);
 	}