commit 01de33e91f9717d0cbae5af6eee2beb45deee219
Author: Miroslav Lichvar <mlichvar@redhat.com>
Date:   Tue Mar 4 15:53:37 2025 +0100

    port: Refresh link status on faults.
    
    ptp4l gets the ENOBUFS error on the netlink socket when the kernel has
    to drop messages due to full socket buffer. If ptp4l has a port in the
    faulty state waiting for the link to go up and that event corresponds
    to one of the dropped netlink messages, the port will be stuck in the
    faulty state until the link goes down and up again.
    
    To prevent the port from getting stuck, request the current link status
    when dispatching the EV_FAULT_DETECTED event. Also, reopen the socket to
    get rid of the buffered messages when handling the fault and again when
    reinitializing the port.
    
    Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
    Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

diff --git a/port.c b/port.c
index 7f945ac..1bb407c 100644
--- a/port.c
+++ b/port.c
@@ -1975,6 +1975,20 @@ static int port_cmlds_initialize(struct port *p)
 	return port_cmlds_renew(p, now.tv_sec);
 }
 
+static void port_rtnl_initialize(struct port *p)
+{
+	/* Reopen the socket to get rid of buffered messages */
+	if (p->fda.fd[FD_RTNL] >= 0) {
+		rtnl_close(p->fda.fd[FD_RTNL]);
+	}
+	p->fda.fd[FD_RTNL] = rtnl_open();
+	if (p->fda.fd[FD_RTNL] >= 0) {
+		rtnl_link_query(p->fda.fd[FD_RTNL], interface_name(p->iface));
+	}
+
+	clock_fda_changed(p->clock);
+}
+
 void port_disable(struct port *p)
 {
 	int i;
@@ -2087,13 +2101,8 @@ int port_initialize(struct port *p)
 		if (p->bmca == BMCA_NOOP) {
 			port_set_delay_tmo(p);
 		}
-		if (p->fda.fd[FD_RTNL] == -1) {
-			p->fda.fd[FD_RTNL] = rtnl_open();
-		}
-		if (p->fda.fd[FD_RTNL] >= 0) {
-			const char *ifname = interface_name(p->iface);
-			rtnl_link_query(p->fda.fd[FD_RTNL], ifname);
-		}
+
+		port_rtnl_initialize(p);
 	}
 
 	port_nrate_initialize(p);
@@ -3768,6 +3777,13 @@ int port_state_update(struct port *p, enum fsm_event event, int mdiff)
 		if (port_link_status_get(p) && clear_fault_asap(&i)) {
 			pr_notice("%s: clearing fault immediately", p->log_name);
 			next = p->state_machine(next, EV_FAULT_CLEARED, 0);
+		} else if (event == EV_FAULT_DETECTED) {
+			/*
+			 * Reopen the netlink socket and refresh the link
+			 * status in case the fault was triggered by a missed
+			 * netlink message (ENOBUFS).
+			 */
+			port_rtnl_initialize(p);
 		}
 	}