RDS: RDS-core fixes

This patch-series updates the RDS core and rds-tcp modules with some bug fixes that were originally authored by Andy Grover, Zach Brown, and Chris Mason.

v5: Clarify comment per http://www.spinics.net/lists/netdev/msg324220.html

Sowmini Varadhan (3):
Document AF_RDS, PF_RDS and SOL_RDS correctly.
RDS: only use passive connections when addresses match
RDS: make sure not to loop forever inside rds_send_xmit

 Documentation/networking/rds.txt |    9 ++++-----
 net/rds/connection.c             |    3 ++-
 net/rds/rds.h                    |    1 +
 net/rds/send.c                   |   33 +++++++++++++++++++++++++++++++--
 4 files changed, 38 insertions(+), 8 deletions(-)

AF_RDS, PF_RDS and SOL_RDS are available in header files, and there is no need to get their values from /proc. Document this correctly.

---
v4: this change replaces the v3 modifications to sysctl.c

 Documentation/networking/rds.txt |    9 ++++-----
 1 files changed, 4 insertions(+), 5 deletions(-)

index c67077c..e1a3d59 100644
@@ -62,11 +62,10 @@ Socket Interface
 ================
 
   AF_RDS, PF_RDS, SOL_RDS
-        These constants haven't been assigned yet, because RDS isn't in
-        mainline yet. Currently, the kernel module assigns some constant
-        and publishes it to user space through two sysctl files
-                /proc/sys/net/rds/pf_rds
-                /proc/sys/net/rds/sol_rds
+	AF_RDS and PF_RDS are the domain type to be used with socket(2)
+	to create RDS sockets. SOL_RDS is the socket-level to be used
+	with setsockopt(2) and getsockopt(2) for RDS specific socket
+	options.
 
   fd = socket(PF_RDS, SOCK_SEQPACKET, 0);
         This creates a new, unbound RDS socket.

1.7.1

Passive connections were added for the case where one loopback IB connection between identical addresses needs another connection to store the second QP. Unfortunately, they were also created in the case where the addesses differ and we already have both QPs.

This lead to a message reordering bug.

- two different IB interfaces and addresses on a machine: A B
- traffic is sent from A to B
- connection from A-B is created, connect request sent
- listening accepts connect request, B-A is created
- traffic flows, next_rx is incremented
- unacked messages exist on the retrans list
- connection A-B is shut down, new connect request sent
- listen sees existing loopback B-A, creates new passive B-A
- retrans messages are sent and delivered because of 0 next_rx

The problem is that the second connection request saw the previously existing parent connection. Instead of using it, and using the existing next_rx_seq state for the traffic between those IPs, it mistakenly thought that it had to create a passive connection.

We fix this by only using passive connections in the special case where laddr and faddr match. In this case we'll only ever have one parent sending connection requests and one passive connection created as the listening path sees the existing parent connection which initiated the request.

Original patch by Zach Brown

---
 net/rds/connection.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 378c3a6..7952a5b 100644
@@ -130,7 +130,7 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
 	rcu_read_lock();
 	conn = rds_conn_lookup(head, laddr, faddr, trans);
 	if (conn && conn->c_loopback && conn->c_trans != &rds_loop_transport &&
-	    !is_outgoing) {
+	    laddr == faddr && !is_outgoing) {
 		/* This is a looped back IB connection, and we're
 		 * called by the code handling the incoming connect.
 		 * We need a second connection object into which we

1.7.1

If a determined set of concurrent senders keep the send queue full, we can loop forever inside rds_send_xmit. This fix has two parts.

First we are dropping out of the while(1) loop after we've processed a large batch of messages.

Second we add a generation number that gets bumped each time the xmit bit lock is acquired. If someone else has jumped in and made progress in the queue, we skip our goto restart.

Original patch by Chris Mason.

---
v5: Modified comment per DaveM feedback

 net/rds/connection.c |    1 +
 net/rds/rds.h        |    1 +
 net/rds/send.c       |   33 +++++++++++++++++++++++++++++++--
 3 files changed, 33 insertions(+), 2 deletions(-)

index 7952a5b..14f0413 100644
@@ -193,6 +193,7 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
 	}
 
 	atomic_set(&conn->c_state, RDS_CONN_DOWN);
+	conn->c_send_gen = 0;
 	conn->c_reconnect_jiffies = 0;
 	INIT_DELAYED_WORK(&conn->c_send_w, rds_send_worker);
 	INIT_DELAYED_WORK(&conn->c_recv_w, rds_recv_worker);

index c3f2855..0d41155 100644
@@ -110,6 +110,7 @@ struct rds_connection {
 	void			*c_transport_data;
 
 	atomic_t		c_state;
+	unsigned long		c_send_gen;
 	unsigned long		c_flags;
 	unsigned long		c_reconnect_jiffies;
 	struct delayed_work	c_send_w;

index 44672be..e9430f5 100644
@@ -140,8 +140,11 @@ int rds_send_xmit(struct rds_connection *conn)
 	struct scatterlist *sg;
 	int ret = 0;
 	LIST_HEAD(to_be_dropped);
+	int batch_count;
+	unsigned long send_gen = 0;
 
 restart:
+	batch_count = 0;
 
 	/*
 	 * sendmsg calls here after having queued its message on the send

@@ -157,6 +160,17 @@ int rds_send_xmit(struct rds_connection *conn)
 	}
 
 	/*
+	 * we record the send generation after doing the xmit acquire.
+	 * if someone else manages to jump in and do some work, we'll use
+	 * this to avoid a goto restart farther down.
+	 *
+	 * The acquire_in_xmit() check above ensures that only one
+	 * caller can increment c_send_gen at any time.
+	 */
+	conn->c_send_gen++;
+	send_gen = conn->c_send_gen;
+
+	/*
 	 * rds_conn_shutdown() sets the conn state and then tests RDS_IN_XMIT,
 	 * we do the opposite to avoid races.
 	 */

@@ -202,6 +216,16 @@ int rds_send_xmit(struct rds_connection *conn)
 		if (!rm) {
 			unsigned int len;
 
+			batch_count++;
+
+			/* we want to process as big a batch as we can, but
+			 * we also want to avoid softlockups.  If we've been
+			 * through a lot of messages, lets back off and see
+			 * if anyone else jumps in
+			 */
+			if (batch_count >= 1024)
+				goto over_batch;
+
 			spin_lock_irqsave(&conn->c_lock, flags);
 
 			if (!list_empty(&conn->c_send_queue)) {

@@ -357,9 +381,9 @@ int rds_send_xmit(struct rds_connection *conn)
 		}
 	}
 
+over_batch:
 	if (conn->c_trans->xmit_complete)
 		conn->c_trans->xmit_complete(conn);
-
 	release_in_xmit(conn);
 
 	/* Nuke any messages we decided not to retransmit. */

@@ -380,10 +404,15 @@ int rds_send_xmit(struct rds_connection *conn)
 	 * If the transport cannot continue (i.e ret != 0), then it must
 	 * call us when more room is available, such as from the tx
 	 * completion handler.
+	 *
+	 * We have an extra generation check here so that if someone manages
+	 * to jump in after our release_in_xmit, we'll see that they have done
+	 * some work and we will skip our goto
 	 */
 	if (ret == 0) {
 		smp_mb();
-		if (!list_empty(&conn->c_send_queue)) {
+		if (!list_empty(&conn->c_send_queue) &&
+		    send_gen == conn->c_send_gen) {
 			rds_stats_inc(s_send_lock_queue_raced);
 			goto restart;
 		}

1.7.1

From: Sowmini Varadhan <[email protected]>
Date: Wed, 8 Apr 2015 09:46:08 -0400

Where are the v2, v3, v4 etc. notes?

Please don't remove them, I put them into the merge commit message and they help people reading it understand how a patch series evolved into it's final state.

This is so tiring... please submit this again with the missing information put back.

Thanks.

From: Sowmini Varadhan <[email protected]>
Date: Wed, 8 Apr 2015 12:33:44 -0400

Series applied, thanks.