Re: [RFC PATCH 06/10] net: add SO_DEVMEM_DONTNEED setsockopt to release RX pages

[Andy Lutomirski <luto@kernel.org>]

On 7/10/23 15:32, Mina Almasry wrote:
> Add an interface for the user to notify the kernel that it is done reading
> the NET_RX dmabuf pages returned as cmsg. The kernel will drop the
> reference on the NET_RX pages to make them available for re-use.
> 
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> ---

> +		for (i = 0; i < num_tokens; i++) {
> +			for (j = 0; j < tokens[i].token_count; j++) {
> +				struct page *pg = xa_erase(&sk->sk_pagepool,
> +							   tokens[i].token_start + j);
> +
> +				if (pg)
> +					put_page(pg);
> +				else
> +					/* -EINTR here notifies the userspace
> +					 * that not all tokens passed to it have
> +					 * been freed.
> +					 */
> +					ret = -EINTR;

Unless I'm missing something, this type of error reporting is 
unrecoverable -- userspace doesn't know how many tokens have been freed.

I think you should either make it explicitly unrecoverable (somehow shut 
down dmabuf handling entirely) or tell userspace how many tokens were 
successfully freed.

--Andy