Re: [PATCH net 1/1] net: devmem: prevent net-iov / page mixing

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Wed, Jul 22, 2026 at 11:58:46AM +0100, Pavel Begunkov wrote:
> We should either have net_iov or page backed frags in a single skb,
> otherwise it blows up down the stack. Don't allow mixing in
> zerocopy_fill_skb_from_devmem().
> 
> Fixes: bd61848900bff ("net: devmem: Implement TX path")
> Cc: stable@vger.kernel.org
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  net/core/datagram.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/core/datagram.c b/net/core/datagram.c
> index c285c6465923..35febc1c25fa 100644
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -712,6 +712,9 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from,
>  	size_t virt_addr, size, off;
>  	struct net_iov *niov;
>  
> +	if (i && skb_frags_readable(skb))
> +		return -EEXIST;

Are we trying to hit the -EEXIST handler in tcp_sendmsg_locked() so that
we start a new skb? If so, I think we might need to plumb this -EEXIST
case through skb_zerocopy_iter_stream() too?

Best,
Bobby