[PATCH RFC] RDMA/CMA: Allocate PS_TCP ports from the host TCP port space.

[Steve Wise <swise@opengridcomputing.com>]

Networking experts,

I'd like input on the patch below, and help in solving this bug 
properly.  iWARP devices that support both native stack TCP and iWARP 
(aka RDMA over TCP/IP/Ethernet) connections on the same interface need 
the fix below or some similar fix to the RDMA connection manager.

This is a BUG in the Linux RDMA-CMA code as it stands today.

Here is the issue:

Consider an mpi cluster running mvapich2.  And the cluster runs 
MPI/Sockets jobs concurrently with MPI/RDMA jobs.  It is possible, 
without the patch below, for MPI/Sockets processes to mistakenly get 
incoming RDMA connections and vice versa.  The way mvapich2 works is 
that the ranks all bind and listen to a random port (retrying new random 
ports if the bind fails with "in use").  Once they get a free port and
bind/listen, they advertise that port number to the peers to do 
connection setup.  Currently, without the patch below, the mpi/rdma 
processes can end up binding/listening to the _same_ port number as the 
mpi/sockets processes running over the native tcp stack.  This is due to 
duplicate port spaces for native stack TCP and the rdma cm's RDMA_PS_TCP 
port space.  If this happens, then the connections can get screwed up.

The correct solution in my mind is to use the host stack's TCP port 
space for _all_ RDMA_PS_TCP port allocations.   The patch below is a 
minimal delta to unify the port spaces by using the kernel stack to bind 
ports.  This is done by allocating a kernel socket and binding to the 
appropriate local addr/port.  It also allows the kernel stack to pick 
ephemeral ports by virtue of just passing in port 0 on the kernel bind 
operation.

There has been a discussion already on the RDMA list if anyone is 
interested:

http://www.mail-archive.com/general@lists.openfabrics.org/msg05162.html


Thanks,

Steve.


---

RDMA/CMA: Allocate PS_TCP ports from the host TCP port space.

This is needed for iwarp providers that support native and rdma
connections over the same interface.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
---

drivers/infiniband/core/cma.c |   27 ++++++++++++++++++++++++++-
1 files changed, 26 insertions(+), 1 deletions(-)

diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
index 9e0ab04..e4d2d7f 100644
--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -111,6 +111,7 @@ struct rdma_id_private {
	struct rdma_cm_id	id;

	struct rdma_bind_list	*bind_list;
+	struct socket		*sock;
	struct hlist_node	node;
	struct list_head	list;
	struct list_head	listen_list;
@@ -695,6 +696,8 @@ static void cma_release_port(struct rdma
		kfree(bind_list);
	}
	mutex_unlock(&lock);
+	if (id_priv->sock)
+		sock_release(id_priv->sock);
}

void rdma_destroy_id(struct rdma_cm_id *id)
@@ -1790,6 +1793,25 @@ static int cma_use_port(struct idr *ps,
	return 0;
}

+static int cma_get_tcp_port(struct rdma_id_private *id_priv)
+{
+	int ret;
+	struct socket *sock;
+
+	ret = sock_create_kern(AF_INET, SOCK_STREAM, IPPROTO_TCP, &sock);
+	if (ret)
+		return ret;
+	ret = sock->ops->bind(sock,
+			  (struct socketaddr *)&id_priv->id.route.addr.src_addr,
+			  ip_addr_size(&id_priv->id.route.addr.src_addr));
+	if (ret) {
+		sock_release(sock);
+		return ret;
+	}
+	id_priv->sock = sock;
+	return 0;	
+}
+
static int cma_get_port(struct rdma_id_private *id_priv)
{
	struct idr *ps;
@@ -1801,6 +1823,9 @@ static int cma_get_port(struct rdma_id_p
		break;
	case RDMA_PS_TCP:
		ps = &tcp_ps;
+		ret = cma_get_tcp_port(id_priv); /* Synch with native stack */
+		if (ret)
+			goto out;
		break;
	case RDMA_PS_UDP:
		ps = &udp_ps;
@@ -1815,7 +1840,7 @@ static int cma_get_port(struct rdma_id_p
	else
		ret = cma_use_port(ps, id_priv);
	mutex_unlock(&lock);
-
+out:
	return ret;
}


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