[PATCH net v2 3/3] bonding: 3ad: fix stuck negotiation on recovery

[Louis Scalbert <louis.scalbert@6wind.com>]

The previous commit introduced a side effect caused by clearing the
SELECTED flag on disabled ports. After all ports in an aggregator go
down, if only a subset of ports comes back up, those ports can no
longer renegotiate LACP unless all aggregator ports come back up.

1. All aggregator ports go down
  - The SELECTED flag is cleared on all of them.
2. One port comes back up
  - Its SELECTED flag is set again.
  - It enters the WAITING state and gets its READY_N flag.
  - The remaining ports stay UNSELECTED. Because of that, they cannot
  enter the WAITING state and therefore never get READY_N.
  - __agg_ports_are_ready() returns 0 because it finds a port without
  READY_N.
  - As a result, __set_agg_ports_ready() keeps the READY flag cleared on
  all ports.
  - The port that came back up is therefore not marked READY and cannot
  transition to ATTACHED.
  - LACP negotiation becomes stuck, and the port cannot be used.
3. All aggregator ports come back up
  - They all regain SELECTED and READY_N.
  - __agg_ports_are_ready() now returns 1.
  - __set_agg_ports_ready() sets READY on all ports.
  - They can then transition to ATTACHED.
  - Negotiation resumes and the aggregator becomes operational again.

Consider only ports currently in the WAITING mux state for READY_N in
order to avoid __agg_ports_are_ready() to return 0 because of a disabled
port. That matches 802.3ad, which states: "The Selection Logic asserts
Ready TRUE when the values of Ready_N for all ports that are waiting to
attach to a given Aggregator are TRUE.".

Fixes: 655f8919d549 ("bonding: add min links parameter to 802.3ad")
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>
---
 drivers/net/bonding/bond_3ad.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
index 1771e406224c..86657de7143d 100644
--- a/drivers/net/bonding/bond_3ad.c
+++ b/drivers/net/bonding/bond_3ad.c
@@ -700,7 +700,8 @@ static void __update_ntt(struct lacpdu *lacpdu, struct port *port)
 }
 
 /**
- * __agg_ports_are_ready - check if all ports in an aggregator are ready
+ * __agg_ports_are_ready - check if all ports in an aggregator that are in
+ * the WAITING state are ready
  * @aggregator: the aggregator we're looking at
  *
  */
@@ -716,6 +717,8 @@ static int __agg_ports_are_ready(struct aggregator *aggregator)
 		for (port = aggregator->lag_ports;
 		     port;
 		     port = port->next_port_in_aggregator) {
+			if (port->sm_mux_state != AD_MUX_WAITING)
+				continue;
 			if (!(port->sm_vars & AD_PORT_READY_N)) {
 				retval = 0;
 				break;
-- 
2.39.2