git: 3cbc8109a985 - stable/12 - lacp: short timeout erroneously declares link-flapping

The branch stable/12 has been updated by rpokala:

URL: https://cgit.FreeBSD.org/src/commit/?id=3cbc8109a9855edfa24425e7ed7abafa2300148a

commit 3cbc8109a9855edfa24425e7ed7abafa2300148a
Author:     Greg Foster <gfoster@panasas.com>
AuthorDate: 2022-04-26 06:38:23 +0000
Commit:     Ravi Pokala <rpokala@FreeBSD.org>
CommitDate: 2022-05-01 19:16:53 +0000

    lacp: short timeout erroneously declares link-flapping
    
    Panasas was seeing a higher-than-expected number of link-flap events.
    After joint debugging with the switch vendor, we determined there were
    problems on both sides; either of which might cause the occasional
    event, but together caused lots of them.
    
    On the switch side, an internal queuing issue was causing LACP PDUs --
    which should be sent every second, in short-timeout mode -- to sometimes
    be sent slightly later than they should have been. In some cases, two
    successive PDUs were late, but we never saw three late PDUs in a row.
    
    On the FreeBSD side, we saw a link-flap event every time there were two
    late PDUs, while the spec says that it takes *three* seconds of downtime
    to trigger that event. It turns out that if a PDU was received shortly
    before the timer code was run, it would decrement less than a full
    second after the PDU arrived. Then two delayed PDUs would cause two
    additional decrements, causing it to reach zero less than three seconds
    after the most-recent on-time PDU.
    
    The solution is to note the time a PDU arrives, and only decrement if at
    least a full second has elapsed since then.
    
    Reported by:    Greg Foster <gfoster@panasas.com>
    Reviewed by:    gallatin
    Tested by:      Greg Foster <gfoster@panasas.com>
    MFC after:      3 days
    Sponsored by:   Panasas
    Differential Revision:  https://reviews.freebsd.org/D35070
    
    (cherry picked from commit 00a80538b4471b2978c5a1990f48189f2c692e24)
---
 sys/net/ieee8023ad_lacp.c | 18 ++++++++++++++++--
 sys/net/ieee8023ad_lacp.h |  1 +
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/sys/net/ieee8023ad_lacp.c b/sys/net/ieee8023ad_lacp.c
index 1bdc2d8b852c..61cd94e5ce2f 100644
--- a/sys/net/ieee8023ad_lacp.c
+++ b/sys/net/ieee8023ad_lacp.c
@@ -48,6 +48,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/lock.h>
 #include <sys/rwlock.h>
 #include <sys/taskqueue.h>
+#include <sys/time.h>
 
 #include <net/if.h>
 #include <net/if_var.h>
@@ -1704,6 +1705,7 @@ lacp_sm_rx(struct lacp_port *lp, const struct lacpdu *du)
 	 * EXPIRED, DEFAULTED, CURRENT -> CURRENT
 	 */
 
+	microuptime(&lp->lp_last_lacpdu_rx);
 	lacp_sm_rx_update_selected(lp, du);
 	lacp_sm_rx_update_ntt(lp, du);
 	lacp_sm_rx_record_pdu(lp, du);
@@ -1913,14 +1915,26 @@ static void
 lacp_run_timers(struct lacp_port *lp)
 {
 	int i;
+	struct timeval time_diff;
 
 	for (i = 0; i < LACP_NTIMER; i++) {
 		KASSERT(lp->lp_timer[i] >= 0,
 		    ("invalid timer value %d", lp->lp_timer[i]));
 		if (lp->lp_timer[i] == 0) {
 			continue;
-		} else if (--lp->lp_timer[i] <= 0) {
-			if (lacp_timer_funcs[i]) {
+		} else {
+			if (i == LACP_TIMER_CURRENT_WHILE) {
+				microuptime(&time_diff);
+				timevalsub(&time_diff, &lp->lp_last_lacpdu_rx);
+				if (time_diff.tv_sec) {
+					/* At least one sec has elapsed since last LACP packet. */
+					--lp->lp_timer[i];
+				}
+			} else {
+				--lp->lp_timer[i];
+			}
+
+			if ((lp->lp_timer[i] <= 0) && (lacp_timer_funcs[i])) {
 				(*lacp_timer_funcs[i])(lp);
 			}
 		}
diff --git a/sys/net/ieee8023ad_lacp.h b/sys/net/ieee8023ad_lacp.h
index 5ae48cebb62d..10c6a2c9f892 100644
--- a/sys/net/ieee8023ad_lacp.h
+++ b/sys/net/ieee8023ad_lacp.h
@@ -215,6 +215,7 @@ struct lacp_port {
 #define	lp_key		lp_actor.lip_key
 #define	lp_systemid	lp_actor.lip_systemid
 	struct timeval		lp_last_lacpdu;
+	struct timeval		lp_last_lacpdu_rx;
 	int			lp_lacpdu_sent;
 	enum lacp_mux_state	lp_mux_state;
 	enum lacp_selected	lp_selected;