>dev))) { ... }
    - This ensures redirection also when `!netif_running()`
      (administratively down).
  - The reason blackholing occurs without this patch:
    - On STP port disable, FDB entries are not flushed if a backup port
      is configured:
      - net/bridge/br_stp_if.c:116
        if (!rcu_access_pointer(p->backup_port))
        br_fdb_delete_by_port(br, p, 0, 0);
    - This optimization (commit 8dc350202d32, “optimize backup_port fdb
      convergence”) intentionally keeps FDB entries to enable seamless
      redirection, but br_forward() fails to redirect when the port is
      admin down, causing drops.

- Risk assessment
  - Minimal regression risk: Checks only `netif_running(to->dev)` in a
    path that already conditionally redirects; `should_deliver()` still
    gates actual forwarding on the backup port’s state and policy.
  - No new features, no data structure changes, no timing-sensitive
    logic added.
  - Behavior remains unchanged unless a backup port is configured, and
    then only in the admin-down case, which is the intended failover
    scenario.

- Backport considerations
  - Applicable to stable series that include backup port support and the
    FDB-retention optimization (e.g., post-2018/2019 kernels). It will
    not apply to trees that predate `backup_port`.
  - The change is a clean one-liner in `br_forward()`; no dependencies
    beyond existing `netif_running()` and `netif_carrier_ok()`.

Conclusion: This is a clear bugfix to prevent data-plane blackholes in a
supported configuration with minimal risk. It should be backported to
stable kernels that have bridge backup-port support.

 net/bridge/br_forward.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index 29097e984b4f7..870bdf2e082c4 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -148,7 +148,8 @@ void br_forward(const struct net_bridge_port *to,
 		goto out;
 
 	/* redirect to backup link if the destination port is down */
-	if (rcu_access_pointer(to->backup_port) && !netif_carrier_ok(to->dev)) {
+	if (rcu_access_pointer(to->backup_port) &&
+	    (!netif_carrier_ok(to->dev) || !netif_running(to->dev))) {
 		struct net_bridge_port *backup_port;
 
 		backup_port = rcu_dereference(to->backup_port);
-- 
2.51.0[PATCH AUTOSEL 6.17-5.4] bridge: Redirect to backup port when port is administratively downSasha Levin <sashal@kernel.org> undefinedpatches@lists.linux.dev, stable@vger.kernel.org undefined undefined undefined undefined undefined undefined undefined undefined�l��