[PATCH net-next 2/2] net: dsa: user: document the write memory barrier on LAG conduit migration

[Kai Kuang]

The wmb() orders the dp->cpu_dp stores before the new lag_dev->dsa_ptr
is published to the concurrent RX path readers. Document this, since a
plain barrier without a comment is hard to interpret.

Signed-off-by: Kai Kuang <kuangkai@xxxxxxxxxx>
---
 net/dsa/user.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/dsa/user.c b/net/dsa/user.c
index cfad269be75c..96393d4b5da1 100644
--- a/net/dsa/user.c
+++ b/net/dsa/user.c
@@ -3435,6 +3435,10 @@ static void dsa_conduit_lag_leave(struct net_device *conduit,
 		 * physical CPU port
 		 */
 		lag_dev->dsa_ptr = new_cpu_dp;
+		/* Ensure the new dp->cpu_dp values are visible to concurrent
+		 * RX path readers of lag_dev->dsa_ptr before the pointer
+		 * itself becomes visible
+		 */
 		wmb();
 	} else {
 		/* If the LAG DSA conduit has no ports left, migrate back all
-- 
2.25.1


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