[PATCH net v4 2/2] net/rds: don't let the rdma_cm destroy an id RDS still owns on route failure

[Allison Henderson <achender@kernel.org>]

rds_rdma_cm_event_handler_cmn() hands the return value of
rdma_resolve_route() straight back to the rdma_cm on
RDMA_CM_EVENT_ADDR_RESOLVED.  A synchronous failure there - -ENOMEM
from the route work allocation, an SA query that cannot be set up, a
RoCE route with no usable device - makes addr_handler() destroy the
id the event was delivered on.  That id is ic->i_cm_id, and nothing
clears the pointer: the connection sits in RDS_CONN_CONNECTING with a
freed id until its shutdown calls rdma_disconnect() and
rdma_destroy_id() on it.

The ROUTE_RESOLVED case already avoids this: rds_ib_cm_initiate_connect()
forces a zero return while ic->i_cm_id == cm_id, as the comment there
explains.  Do the same here - drop the connection and return 0 - so
the id stays RDS's to destroy from the shutdown, and the reconnect
gets a fresh one.

Fixes: 55b7ed0b582f ("RDS: Common RDMA transport code")
Assisted-by: Claude-Code:claude-fable-5
Signed-off-by: Allison Henderson <achender@kernel.org>
---
 net/rds/rdma_transport.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/net/rds/rdma_transport.c b/net/rds/rdma_transport.c
index 09cc2ba23570..7be38be1228e 100644
--- a/net/rds/rdma_transport.c
+++ b/net/rds/rdma_transport.c
@@ -107,9 +107,19 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
 			}
 			rdma_set_service_type(cm_id, conn->c_tos);
 			rdma_set_min_rnr_timer(cm_id, IB_RNR_TIMER_000_32);
-			/* XXX do we need to clean up if this fails? */
 			ret = rdma_resolve_route(cm_id,
 						 RDS_RDMA_RESOLVE_TIMEOUT_MS);
+			if (ret) {
+				/* A non-zero return has the rdma_cm destroy
+				 * the id, but it is still ic->i_cm_id, which
+				 * the connection's shutdown would then
+				 * disconnect and destroy again.  Drop the
+				 * connection and keep the id for that
+				 * shutdown.
+				 */
+				rds_conn_drop(conn);
+				ret = 0;
+			}
 		}
 		break;
 
-- 
2.25.1