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

Kuniyuki Iwashima
2023-06-07T16:05:58Z

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,
> };