On Mon, Dec 20, 2021 at 10:16:28PM +0800, Greg KH wrote:

Why not return an error?

Because I have received the mail from Martin Habets that telling me
it doesn't need to return error code.
Here is the mail.
https://lore.kernel.org/lkml/20211219092948.t2iprptmyfrzgthb@gmail.com/ (local)
On Sun, Dec 19, 2021 at 05:29:48PM +0800, Martin Habets wrote:

Your predicate is wrong. The code that uses rx_queue->page_ring
can deal with it being NULL.
The only thing you might want to do is set rx_queue->page_ptr_mask
to 0.

Jiasheng