Re: [PATCH 4/4] net/tls: implement ->read_sock()

[Sagi Grimberg <sagi@grimberg.me>]

> Implement ->read_sock() function for use with nvme-tcp.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
> Cc: Boris Pismenny <boris.pismenny@gmail.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: netdev@vger.kernel.org
> ---
>   net/tls/tls.h      |  2 ++
>   net/tls/tls_main.c |  2 ++
>   net/tls/tls_sw.c   | 78 ++++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 82 insertions(+)
> 
> diff --git a/net/tls/tls.h b/net/tls/tls.h
> index d002c3af1966..ba55cd5c4913 100644
> --- a/net/tls/tls.h
> +++ b/net/tls/tls.h
> @@ -114,6 +114,8 @@ bool tls_sw_sock_is_readable(struct sock *sk);
>   ssize_t tls_sw_splice_read(struct socket *sock, loff_t *ppos,
>   			   struct pipe_inode_info *pipe,
>   			   size_t len, unsigned int flags);
> +int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
> +		     sk_read_actor_t read_actor);
>   
>   int tls_device_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
>   void tls_device_splice_eof(struct socket *sock);
> diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> index 7b9c83dd7de2..1a062a8c6d33 100644
> --- a/net/tls/tls_main.c
> +++ b/net/tls/tls_main.c
> @@ -963,10 +963,12 @@ static void build_proto_ops(struct proto_ops ops[TLS_NUM_CONFIG][TLS_NUM_CONFIG]
>   	ops[TLS_BASE][TLS_SW  ] = ops[TLS_BASE][TLS_BASE];
>   	ops[TLS_BASE][TLS_SW  ].splice_read	= tls_sw_splice_read;
>   	ops[TLS_BASE][TLS_SW  ].poll		= tls_sk_poll;
> +	ops[TLS_BASE][TLS_SW  ].read_sock	= tls_sw_read_sock;
>   
>   	ops[TLS_SW  ][TLS_SW  ] = ops[TLS_SW  ][TLS_BASE];
>   	ops[TLS_SW  ][TLS_SW  ].splice_read	= tls_sw_splice_read;
>   	ops[TLS_SW  ][TLS_SW  ].poll		= tls_sk_poll;
> +	ops[TLS_SW  ][TLS_SW  ].read_sock	= tls_sw_read_sock;
>   
>   #ifdef CONFIG_TLS_DEVICE
>   	ops[TLS_HW  ][TLS_BASE] = ops[TLS_BASE][TLS_BASE];
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index 97379e34c997..e918c98bbeb2 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -2231,6 +2231,84 @@ ssize_t tls_sw_splice_read(struct socket *sock,  loff_t *ppos,
>   	goto splice_read_end;
>   }
>   
> +int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
> +		     sk_read_actor_t read_actor)
> +{
> +	struct tls_context *tls_ctx = tls_get_ctx(sk);
> +	struct tls_sw_context_rx *ctx = tls_sw_ctx_rx(tls_ctx);
> +	struct strp_msg *rxm = NULL;
> +	struct tls_msg *tlm;
> +	struct sk_buff *skb;
> +	ssize_t copied = 0;
> +	int err, used;
> +
> +	err = tls_rx_reader_lock(sk, ctx, true);
> +	if (err < 0)
> +		return err;

Unlike recvmsg or splice_read, the caller of read_sock is assumed to
have the socket locked, and tls_rx_reader_lock also calls lock_sock,
how is this not a deadlock?

I'm not exactly clear why the lock is needed here or what is the subtle
distinction between tls_rx_reader_lock and what lock_sock provides.