[PATCH net-next v2 7/9] net/rds: pin the connection across RDMA-CM event handling
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COLD30d
SUPERSEDED
From: Allison Henderson <achender@kernel.org>
Date: 2026-09-12 03:50:32
Also in:
linux-rdma
Subsystem:
networking [general], rds - reliable datagram sockets, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Allison Henderson, Linus Torvalds
Revision v2 of 8 in this series.
Revisions (8)
rds_rdma_cm_event_handler_cmn() picks the connection up from cm_id->context, which carries no reference, and holds c_cm_lock - a mutex that lives in the connection's path array - across the transport callbacks. Now that a connection is freed by its last reference rather than by rds_conn_destroy() itself, a callback that drops the last reference other than the handler's implicit one leaves the final mutex_unlock() running on freed memory. Take a reference for the duration of the handler, and ignore the event if the connection is already being freed: its cm_id teardown is what stops event delivery, so an event that still arrives belongs to a connection whose shutdown has run and whose memory is on its way out. rds_ib_cm_handle_connect() has the mirror-image hole: a connection whose destroy has already quiesced it sits in RDS_CONN_DOWN with no cm_id, which is exactly the state the DOWN -> CONNECTING transition claims. A connect request arriving then would install a new cm_id and QP on a connection that is only waiting for its last reference to go away, and nothing would tear them down again. Re-check rds_destroy_pending() under c_cm_lock and reject the request instead. Assisted-by: Claude-Code:claude-fable-5 Signed-off-by: Allison Henderson <achender@kernel.org> --- net/rds/ib_cm.c | 7 +++++++ net/rds/rdma_transport.c | 16 +++++++++++++++- net/rds/rds.h | 5 +++++ 3 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c
index 01e4b4be979d..323c1eee2777 100644
--- a/net/rds/ib_cm.c
+++ b/net/rds/ib_cm.c@@ -874,6 +874,13 @@ int rds_ib_cm_handle_connect(struct rdma_cm_id *cm_id, * see the comment above rds_queue_reconnect() */ mutex_lock(&conn->c_cm_lock); + /* A destroy that has already quiesced this conn leaves it in + * RDS_CONN_DOWN with no cm_id, exactly what the transition + * below would happily claim; nothing would tear the new cm_id + * and QP down again before the conn is freed. Reject instead. + */ + if (rds_destroy_pending(conn)) + goto out; if (!rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) { if (rds_conn_state(conn) == RDS_CONN_UP) { rdsdebug("incoming connect while connecting\n");
diff --git a/net/rds/rdma_transport.c b/net/rds/rdma_transport.c
index b15cf316b23a..584e9867810f 100644
--- a/net/rds/rdma_transport.c
+++ b/net/rds/rdma_transport.c@@ -63,6 +63,18 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id, if (cm_id->device->node_type == RDMA_NODE_IB_CA) trans = &rds_ib_transport; + /* cm_id->context carries no reference of its own. Pin the + * connection for the duration of the handler: what the callbacks + * below do may drop the last reference other than ours, and the + * mutex released at out: lives in the connection's path array. + * A connection already being freed gets no events handled. + */ + if (conn && !rds_conn_get_unless_zero(conn)) { + rdsdebug("conn %p id %p is being freed, ignoring event\n", + conn, cm_id); + return 0; + } + /* Prevent shutdown from tearing down the connection * while we're executing. */ if (conn) {
@@ -171,8 +183,10 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id, } out: - if (conn) + if (conn) { mutex_unlock(&conn->c_cm_lock); + rds_conn_put(conn); + } rdsdebug("id %p event %u (%s) handling ret %d\n", cm_id, event->event, rdma_event_msg(event->event), ret);
diff --git a/net/rds/rds.h b/net/rds/rds.h
index 4608615e09e9..06d48c2821ef 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h@@ -840,6 +840,11 @@ void rds_conn_shutdown(struct rds_conn_path *cpath); void rds_conn_destroy(struct rds_connection *conn); void rds_conn_get(struct rds_connection *conn); void rds_conn_put(struct rds_connection *conn); +/* take a reference unless the connection is already being freed */ +static inline bool rds_conn_get_unless_zero(struct rds_connection *conn) +{ + return kref_get_unless_zero(&conn->c_refcount); +} /* transport unload waits for its connections to be freed, polling at * the first interval and warning at the second */
--
2.25.1