git: f7735c3952d9 - stable/13 - carp: fix send error demotion recovery

The branch stable/13 has been updated by glebius:

URL: https://cgit.FreeBSD.org/src/commit/?id=f7735c3952d9d54f745f1682ba1f13a70897a8f7

commit f7735c3952d9d54f745f1682ba1f13a70897a8f7
Author:     Gleb Smirnoff <glebius@FreeBSD.org>
AuthorDate: 2021-12-19 01:19:26 +0000
Commit:     Gleb Smirnoff <glebius@FreeBSD.org>
CommitDate: 2022-01-21 18:41:46 +0000

    carp: fix send error demotion recovery
    
    The problem is that carp(4) would clear the error counter on first
    successful send, and stop counting successes after that.  Fix this
    logic and document it in human language.
    
    PR:                     260499
    Differential revision:  https://reviews.freebsd.org/D33536
    
    (cherry picked from commit 9a8cf950b259f6833c7562ce941b0cfeae6687e5)
---
 sys/netinet/ip_carp.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/sys/netinet/ip_carp.c b/sys/netinet/ip_carp.c
index 7554becb974e..71558be619d8 100644
--- a/sys/netinet/ip_carp.c
+++ b/sys/netinet/ip_carp.c
@@ -854,6 +854,13 @@ static void
 carp_send_ad_error(struct carp_softc *sc, int error)
 {
 
+	/*
+	 * We track errors and successfull sends with this logic:
+	 * - Any error resets success counter to 0.
+	 * - MAX_ERRORS triggers demotion.
+	 * - MIN_SUCCESS successes resets error counter to 0.
+	 * - MIN_SUCCESS reverts demotion, if it was triggered before.
+	 */
 	if (error) {
 		if (sc->sc_sendad_errors < INT_MAX)
 			sc->sc_sendad_errors++;
@@ -865,17 +872,17 @@ carp_send_ad_error(struct carp_softc *sc, int error)
 			carp_demote_adj(V_carp_senderr_adj, msg);
 		}
 		sc->sc_sendad_success = 0;
-	} else {
-		if (sc->sc_sendad_errors >= CARP_SENDAD_MAX_ERRORS &&
-		    ++sc->sc_sendad_success >= CARP_SENDAD_MIN_SUCCESS) {
-			static const char fmt[] = "send ok on %s";
-			char msg[sizeof(fmt) + IFNAMSIZ];
-
-			sprintf(msg, fmt, sc->sc_carpdev->if_xname);
-			carp_demote_adj(-V_carp_senderr_adj, msg);
-			sc->sc_sendad_errors = 0;
-		} else
+	} else if (sc->sc_sendad_errors > 0) {
+		if (++sc->sc_sendad_success >= CARP_SENDAD_MIN_SUCCESS) {
+			if (sc->sc_sendad_errors >= CARP_SENDAD_MAX_ERRORS) {
+				static const char fmt[] = "send ok on %s";
+				char msg[sizeof(fmt) + IFNAMSIZ];
+
+				sprintf(msg, fmt, sc->sc_carpdev->if_xname);
+				carp_demote_adj(-V_carp_senderr_adj, msg);
+			}
 			sc->sc_sendad_errors = 0;
+		}
 	}
 }