netdev - [PATCH 4/6] net/rds: No shortcut out of RDS_CONN

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Message-ID: <20250227042638.82553-5-allison.henderson@oracle.com>
Date: Wed, 26 Feb 2025 21:26:36 -0700
From: allison.henderson@...cle.com
To: netdev@...r.kernel.org
Subject: [PATCH 4/6] net/rds: No shortcut out of RDS_CONN_ERROR

From: Gerd Rausch <gerd.rausch@...cle.com>

RDS connections carry a state "rds_conn_path::cp_state"
and transitions from one state to another are conditional
upon an expected state: "rds_conn_path_transition"

There is one exception to this conditionality, which is
"RDS_CONN_ERROR" that can be enforced by "rds_conn_path_drop"
regardless of what state the condition is currently in.

But as soon as a connection enters state "RDS_CONN_ERROR",
the connection handling code expects it to go through the
shutdown-path.

The RDS/TCP multipath changes added a shortcut out of
"RDS_CONN_ERROR" straight back to "RDS_CONN_CONNECTING"
via "rds_tcp_accept_one_path" (e.g. after "rds_tcp_state_change").

A subsequent "rds_tcp_reset_callbacks" can then transition
the state to "RDS_CONN_RESETTING" with a shutdown-worker queued.

That'll trip up "rds_conn_init_shutdown", which was
never adjust to handle "RDS_CONN_RESETTING" and subsequently
drops the connection and leaves "RDS_SHUTDOWN_WORK_QUEUED"
on forever.

So we do two things here:

a) Don't shortcut "RDS_CONN_ERROR", but take the longer
   path through the shutdown code.

b) Add "RDS_CONN_RESETTING" to the expected states in
   "rds_conn_init_shutdown" so that we won't get
   stuck, if we ever hit weird state transitions like
   this again.

Fixes:  ("RDS: TCP: fix race windows in send-path quiescence by rds_tcp_accept_one()")

Signed-off-by: Gerd Rausch <gerd.rausch@...cle.com>
Signed-off-by: Allison Henderson <allison.henderson@...cle.com>
---
 net/rds/connection.c | 2 ++
 net/rds/tcp_listen.c | 5 -----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/rds/connection.c b/net/rds/connection.c
index 84034a3c69bd..b262e6ef6b41 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -382,6 +382,8 @@ void rds_conn_shutdown(struct rds_conn_path *cp)
 		if (!rds_conn_path_transition(cp, RDS_CONN_UP,
 					      RDS_CONN_DISCONNECTING) &&
 		    !rds_conn_path_transition(cp, RDS_CONN_ERROR,
+					      RDS_CONN_DISCONNECTING) &&
+		    !rds_conn_path_transition(cp, RDS_CONN_RESETTING,
 					      RDS_CONN_DISCONNECTING)) {
 			rds_conn_path_error(cp,
 					    "shutdown called in state %d\n",
diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index 60c52322b896..886b5373843e 100644
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -59,9 +59,6 @@ void rds_tcp_keepalive(struct socket *sock)
  * socket and force a reconneect from smaller -> larger ip addr. The reason
  * we special case cp_index 0 is to allow the rds probe ping itself to itself
  * get through efficiently.
- * Since reconnects are only initiated from the node with the numerically
- * smaller ip address, we recycle conns in RDS_CONN_ERROR on the passive side
- * by moving them to CONNECTING in this function.
  */
 static
 struct rds_tcp_connection *rds_tcp_accept_one_path(struct rds_connection *conn)
@@ -86,8 +83,6 @@ struct rds_tcp_connection *rds_tcp_accept_one_path(struct rds_connection *conn)
 		struct rds_conn_path *cp = &conn->c_path[i];

 		if (rds_conn_path_transition(cp, RDS_CONN_DOWN,
-					     RDS_CONN_CONNECTING) ||
-		    rds_conn_path_transition(cp, RDS_CONN_ERROR,
 					     RDS_CONN_CONNECTING)) {
 			return cp->cp_transport_data;
 		}
-- 
2.43.0