Re: [PATCH net-next v5 09/14] kcm: Use splice_eof() to flush

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: David Howells <dhowells@redhat.com>
Date: Wed,  7 Jun 2023 15:05:54 +0100
> Allow splice to undo the effects of MSG_MORE after prematurely ending a
> splice/sendfile due to getting an EOF condition (->splice_read() returned
> 0) after splice had called sendmsg() with MSG_MORE set when the user didn't
> set MSG_MORE.
> 
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Link: https://lore.kernel.org/r/CAHk-=wh=V579PDYvkpnTobCLGczbgxpMgGmmhqiTyE34Cpi5Gg@mail.gmail.com/
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Tom Herbert <tom@herbertland.com>
> cc: Tom Herbert <tom@quantonium.net>
> cc: Cong Wang <cong.wang@bytedance.com>
> cc: Jakub Kicinski <kuba@kernel.org>
> cc: Eric Dumazet <edumazet@google.com>
> cc: "David S. Miller" <davem@davemloft.net>
> cc: Paolo Abeni <pabeni@redhat.com>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: netdev@vger.kernel.org
> ---
>  net/kcm/kcmsock.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
> index ba22af16b96d..d0d8c54562d6 100644
> --- a/net/kcm/kcmsock.c
> +++ b/net/kcm/kcmsock.c
> @@ -968,6 +968,19 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
>  	return err;
>  }
>  
> +static void kcm_splice_eof(struct socket *sock)
> +{
> +	struct sock *sk = sock->sk;
> +	struct kcm_sock *kcm = kcm_sk(sk);
> +
> +	if (skb_queue_empty(&sk->sk_write_queue))

nit: would be better to use skb_queue_empty_lockless().


> +		return;
> +
> +	lock_sock(sk);
> +	kcm_write_msgs(kcm);
> +	release_sock(sk);
> +}
> +
>  static ssize_t kcm_sendpage(struct socket *sock, struct page *page,
>  			    int offset, size_t size, int flags)
>  
> @@ -1773,6 +1786,7 @@ static const struct proto_ops kcm_dgram_ops = {
>  	.sendmsg =	kcm_sendmsg,
>  	.recvmsg =	kcm_recvmsg,
>  	.mmap =		sock_no_mmap,
> +	.splice_eof =	kcm_splice_eof,
>  	.sendpage =	kcm_sendpage,
>  };
>  
> @@ -1794,6 +1808,7 @@ static const struct proto_ops kcm_seqpacket_ops = {
>  	.sendmsg =	kcm_sendmsg,
>  	.recvmsg =	kcm_recvmsg,
>  	.mmap =		sock_no_mmap,
> +	.splice_eof =	kcm_splice_eof,
>  	.sendpage =	kcm_sendpage,
>  	.splice_read =	kcm_splice_read,
>  };