[PATCH net 3/3] net/rds: fix rds_message leak in the rds_send_xmit() drop path

[Allison Henderson <achender@kernel.org>]

From: Sharath Srinivasan <sharath.srinivasan@oracle.com>

When rds_send_xmit() picks the next message off cp_send_queue it takes
its own reference with rds_message_addref().  If the message then hits
the never-retransmit check (RDS_MSG_FLUSH, or an RDMA op that was
already retransmitted), it is moved to the local to_be_dropped list and
that reference is dropped after the batch.

However, if RDS_MSG_ON_CONN has already been cleared - e.g. a racing
rds_send_drop_to() or rds_send_path_reset() took the message off the
connection lists - the message is not added to to_be_dropped and the
reference taken above is never dropped: cp_xmit_rm has not been set at
this point, so the loop simply abandons rm and the rds_message (and
everything it pins: pages, MRs, notifiers) leaks after an RDMA error.

Drop the reference directly in that case.

This mirrors Oracle UEK commit "net/rds: fix rds_message memleak in
rds_send_xmit".

Fixes: 2ad8099b58f2 ("RDS: rds_send_xmit() locking/irq fixes")
Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Signed-off-by: Sharath Srinivasan <sharath.srinivasan@oracle.com>
[achender: port to net-next; update commit message]
Assisted-by: Claude-Code:claude-fable-5
Signed-off-by: Allison Henderson <achender@kernel.org>
---
 net/rds/send.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/rds/send.c b/net/rds/send.c
index 68be1bf0e0adf..ab3a8366c53bd 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -339,9 +339,17 @@ int rds_send_xmit(struct rds_conn_path *cp)
 			    (rm->rdma.op_active &&
 			    test_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags))) {
 				spin_lock_irqsave(&cp->cp_lock, flags);
-				if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags))
+				if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags)) {
+					/* our ref is put after the batch */
 					list_move(&rm->m_conn_item, &to_be_dropped);
-				spin_unlock_irqrestore(&cp->cp_lock, flags);
+					spin_unlock_irqrestore(&cp->cp_lock, flags);
+				} else {
+					/* already off the conn list; drop
+					 * the ref taken above ourselves
+					 */
+					spin_unlock_irqrestore(&cp->cp_lock, flags);
+					rds_message_put(rm);
+				}
 				continue;
 			}
 
-- 
2.25.1