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[195.231.45.245]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49ccd1e19desm322712395e9.1.2026.09.01.04.32.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Sep 2026 04:32:55 -0700 (PDT) Message-ID: <06d2e605-6d3d-40f0-b247-031756c0d752@redhat.com> Date: Tue, 1 Sep 2026 13:32:54 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] bonding: avoid ARP flood on RTNL contention in active-backup mode To: Eric Dumazet , "David S . Miller" , Jakub Kicinski , Jay Vosburgh Cc: Simon Horman , Andrew Lunn , netdev@vger.kernel.org, eric.dumazet@gmail.com, Tonghao Zhang , Hangbin Liu References: <20260831090937.3342052-1-edumazet@google.com> From: Paolo Abeni Content-Language: en-US In-Reply-To: <20260831090937.3342052-1-edumazet@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/31/26 11:09 AM, Eric Dumazet wrote: > Commit f1986b3a9f2e ("net: bonding: skip the 2nd trylock when first one > fail") changed bond_activebackup_arp_mon() to reschedule arp_work in > 1 tick if the second rtnl_trylock() fails (for sending peer/slave > notifications). > > However, by the time bond_activebackup_arp_mon() reaches this second lock > check, bond_ab_arp_probe() has already been executed and sent an ARP probe. > If RTNL remains contended, rescheduling every 1 tick causes > bond_activebackup_arp_mon() to re-execute bond_ab_arp_probe() every jiffy, > flooding the network with ARP probes at HZ frequency (e.g. 1000 pkts/sec) > instead of respecting the configured arp_interval. > > If rtnl_trylock() fails at the second check, do not change delta_in_ticks > to 1 so that the next ARP monitor execution is scheduled according to the > configured arp_interval, matching the behavior in > bond_loadbalance_arp_mon(). > > Fixes: f1986b3a9f2e ("net: bonding: skip the 2nd trylock when first one fail") > Signed-off-by: Eric Dumazet > --- > Cc: Tonghao Zhang > Cc: Hangbin Liu > Cc: Jay Vosburgh > --- > drivers/net/bonding/bond_main.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c > index ef9eb0c53c66..c23cf18a996a 100644 > --- a/drivers/net/bonding/bond_main.c > +++ b/drivers/net/bonding/bond_main.c > @@ -3871,10 +3871,8 @@ static void bond_activebackup_arp_mon(struct bonding *bond) > rcu_read_unlock(); > > if (READ_ONCE(bond->send_peer_notif) || should_notify_rtnl) { > - if (!rtnl_trylock()) { > - delta_in_ticks = 1; > + if (!rtnl_trylock()) > goto re_arm; Sashiko noted this should cause a regression, with notifications potentially delayed for an unbounded time: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260831090937.3342052-1-edumazet%40google.com That was also the behavior prior to f1986b3a9f2e, so I guess is a reasonable trade-off, but a 2nd opinion would help :) /P