Re: [PATCH 4.18 093/150] rds: RDS (tcp) hangs on sendto() to unresponding address

[Ka-Cheong Poon]

On 11/3/18 2:34 AM, Greg Kroah-Hartman wrote:
> 4.18-stable review patch.  If anyone has any objections, please let me know.


This patch has a problem.  I am working on a fix for that.  Please
do not include it in the stable release.  Thanks.


> ------------------
>
> [ Upstream commit 9a4890bd6d6325a1c88564a20ab310b2d56f6094 ]
>
> In rds_send_mprds_hash(), if the calculated hash value is non-zero and
> the MPRDS connections are not yet up, it will wait.  But it should not
> wait if the send is non-blocking.  In this case, it should just use the
> base c_path for sending the message.
>
> Signed-off-by: Ka-Cheong Poon <ka-cheong.poon@xxxxxxxxxx>
> Acked-by: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>   net/rds/send.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/net/rds/send.c b/net/rds/send.c
> index 59f17a2335f4..0e54ca0f4e9e 100644
> --- a/net/rds/send.c
> +++ b/net/rds/send.c
> @@ -1006,7 +1006,8 @@ static int rds_cmsg_send(struct rds_sock *rs, struct rds_message *rm,
>   	return ret;
>   }
>   
> -static int rds_send_mprds_hash(struct rds_sock *rs, struct rds_connection *conn)
> +static int rds_send_mprds_hash(struct rds_sock *rs,
> +			       struct rds_connection *conn, int nonblock)
>   {
>   	int hash;
>   
> @@ -1022,10 +1023,16 @@ static int rds_send_mprds_hash(struct rds_sock *rs, struct rds_connection *conn)
>   		 * used.  But if we are interrupted, we have to use the zero
>   		 * c_path in case the connection ends up being non-MP capable.
>   		 */
> -		if (conn->c_npaths == 0)
> +		if (conn->c_npaths == 0) {
> +			/* Cannot wait for the connection be made, so just use
> +			 * the base c_path.
> +			 */
> +			if (nonblock)
> +				return 0;
>   			if (wait_event_interruptible(conn->c_hs_waitq,
>   						     conn->c_npaths != 0))
>   				hash = 0;
> +		}
>   		if (conn->c_npaths == 1)
>   			hash = 0;
>   	}
> @@ -1170,7 +1177,7 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
>   	}
>   
>   	if (conn->c_trans->t_mp_capable)
> -		cpath = &conn->c_path[rds_send_mprds_hash(rs, conn)];
> +		cpath = &conn->c_path[rds_send_mprds_hash(rs, conn, nonblock)];
>   	else
>   		cpath = &conn->c_path[0];
>   


--
K. Poon
ka-cheong.poon@xxxxxxxxxx