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

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