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Subject: question about bonding mode 4
To:     Jiri Pirko <jiri@resnulli.us>, Jay Vosburgh <j.vosburgh@gmail.com>
References: <20201218193033.6138-1-jarod@redhat.com>
 <20201228101145.GC3565223@nanopsycho.orion>
 <20210107235813.GB29828@redhat.com>
 <20210108131256.GG3565223@nanopsycho.orion>
CC:     "lipeng (Y)" <lipeng321@huawei.com>,
        <linux-kernel@vger.kernel.org>,
        Veaceslav Falico <vfalico@gmail.com>,
        Andy Gospodarek <andy@greyhouse.net>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Thomas Davis <tadavis@lbl.gov>, <netdev@vger.kernel.org>,
        <linuxarm@openeuler.org>, Salil Mehta <salil.mehta@huawei.com>
From:   moyufeng <moyufeng@huawei.com>
Message-ID: <ef692814-fdea-ea59-6b52-93630b5b5570@huawei.com>
Date:   Fri, 15 Jan 2021 10:02:50 +0800
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Hi Team,

I have a question about bonding. During testing bonding mode 4
scenarios, I find that there is a very low probability that
the pointer is null. The following information is displayed:

[99359.795934] bond0: (slave eth13.2001): Port 2 did not find a suitable aggregator
[99359.796960] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
[99359.798127] Mem abort info:
[99359.798526]   ESR = 0x96000004
[99359.798938]   EC = 0x25: DABT (current EL), IL = 32 bits
[99359.799673]   SET = 0, FnV = 0
[99359.800106]   EA = 0, S1PTW = 0
[99359.800554] Data abort info:
[99359.800952]   ISV = 0, ISS = 0x00000004
[99359.801522]   CM = 0, WnR = 0
[99359.801970] user pgtable: 4k pages, 48-bit VAs, pgdp=00000000c64e6000
[99359.802876] [0000000000000020] pgd=0000000000000000
[99359.803555] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[99359.804369] Modules linked in: bonding hns3(-) hclgevf hnae3 [last unloaded: bonding]
[99359.805494] CPU: 1 PID: 951 Comm: kworker/u10:2 Not tainted 5.7.0-rc4+ #1
[99359.806455] Hardware name: linux,dummy-virt (DT)
[99359.807107] Workqueue: bond0 bond_3ad_state_machine_handler [bonding]
[99359.808056] pstate: 60c00005 (nZCv daif +PAN +UAO)
[99359.808722] pc : bond_3ad_state_machine_handler+0x7fc/0xdb8 [bonding]
[99359.809652] lr : bond_3ad_state_machine_handler+0x7f4/0xdb8 [bonding]
[99359.810535] sp : ffff80001882bd20
[99359.811012] x29: ffff80001882bd20 x28: ffff000085939a38
[99359.811791] x27: ffff00008649bb68 x26: 00000000aaaaaaab
[99359.812871] x25: ffff800009401000 x24: ffff800009408de4
[99359.814049] x23: ffff80001882bd98 x22: ffff00008649b880
[99359.815210] x21: 0000000000000000 x20: ffff000085939a00
[99359.816401] x19: ffff00008649b880 x18: ffff800012572988
[99359.817637] x17: 0000000000000000 x16: 0000000000000000
[99359.818870] x15: ffff80009882b987 x14: 726f746167657267
[99359.820090] x13: 676120656c626174 x12: 697573206120646e
[99359.821374] x11: 696620746f6e2064 x10: 696420322074726f
[99359.822659] x9 : 50203a2931303032 x8 : 0000000000081391
[99359.823891] x7 : ffff8000108e3ad0 x6 : ffff8000128858bb
[99359.825109] x5 : 0000000000000000 x4 : 0000000000000000
[99359.826262] x3 : 00000000ffffffff x2 : 906b329bb5362a00
[99359.827394] x1 : 906b329bb5362a00 x0 : 0000000000000000
[99359.828540] Call trace:
[99359.829071]  bond_3ad_state_machine_handler+0x7fc/0xdb8 [bonding]
[99359.830367]  process_one_work+0x15c/0x4a0
[99359.831216]  worker_thread+0x50/0x478
[99359.832022]  kthread+0x130/0x160
[99359.832716]  ret_from_fork+0x10/0x18
[99359.833487] Code: 910c0021 95f704bb f9403f80 b5ffe300 (f9401000)
[99359.834742] ---[ end trace c7a8e02914afc4e0 ]---
[99359.835817] Kernel panic - not syncing: Fatal exception in interrupt
[99359.837334] SMP: stopping secondary CPUs
[99359.838277] Kernel Offset: disabled
[99359.839086] CPU features: 0x080002,22208218
[99359.840053] Memory Limit: none
[99359.840783] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

The test procedure is as follows:
1. Configure bonding and set it to mode 4.
    echo "4" > /sys/class/net/bond0/bonding/mode
    ifconfig bond0 up

2. Configure two VLANs and add them to the bonding in step 1.
    vconfig add eth0 2001
    vconfig add eth1 2001
    ifenslave bond0 eth0.2001 eth1.2001

3. Unload the network device driver and bonding driver.
    rmmod hns3
    rmmod hclge
    rmmod hnae3
    rmmod bonding.ko

4. Repeat the preceding steps for a long time.

By checking the logic in ad_port_selection_logic(), I find that
if enter the branch "Port %d did not find a suitable aggregator",
the value of port->aggregator will be NULL, causing the problem.

So I'd like to ask what circumstances will be involved in this
branch, and what should be done in this case?


The detailed code analysis is as follows:

static void ad_port_selection_logic(struct port *port, bool *update_slave_arr)
{
[...]
	/* if the port is connected to other aggregator, detach it */
	if (port->aggregator) {
		/* detach the port from its former aggregator */
		temp_aggregator = port->aggregator;
		for (curr_port = temp_aggregator->lag_ports; curr_port;
		     last_port = curr_port,
		     curr_port = curr_port->next_port_in_aggregator) {
			if (curr_port == port) {
				temp_aggregator->num_of_ports--;
				/* if it is the first port attached to the
				 * aggregator
				 */
				if (!last_port) {
					temp_aggregator->lag_ports =
						port->next_port_in_aggregator;
				} else {
					/* not the first port attached to the
					 * aggregator
					 */
					last_port->next_port_in_aggregator =
						port->next_port_in_aggregator;
				}

				/* clear the port's relations to this
				 * aggregator
				 */
				port->aggregator = NULL;

----analysis: set port->aggregator NULL at the beginning of ad_port_selection_logic().

				port->next_port_in_aggregator = NULL;
				port->actor_port_aggregator_identifier = 0;

				slave_dbg(bond->dev, port->slave->dev, "Port %d left LAG %d\n",
					  port->actor_port_number,
					  temp_aggregator->aggregator_identifier);
				/* if the aggregator is empty, clear its
				 * parameters, and set it ready to be attached
				 */
				if (!temp_aggregator->lag_ports)
					ad_clear_agg(temp_aggregator);
				break;
			}
		}
		if (!curr_port) {
			/* meaning: the port was related to an aggregator
			 * but was not on the aggregator port list
			 */
			net_warn_ratelimited("%s: (slave %s): Warning: Port %d was related to aggregator %d but was not on its port list\n",
					     port->slave->bond->dev->name,
					     port->slave->dev->name,
					     port->actor_port_number,
					     port->aggregator->aggregator_identifier);
		}
	}
	/* search on all aggregators for a suitable aggregator for this port */
	bond_for_each_slave(bond, slave, iter) {
		aggregator = &(SLAVE_AD_INFO(slave)->aggregator);
		/* keep a free aggregator for later use(if needed) */
		if (!aggregator->lag_ports) {
			if (!free_aggregator)
				free_aggregator = aggregator;

----analysis: Save free_aggregator if found a free aggregator. But in this case, no free aggregator is available.

			continue;
		}
		/* check if current aggregator suits us */
		if (((aggregator->actor_oper_aggregator_key == port->actor_oper_port_key) && /* if all parameters match AND */
		     MAC_ADDRESS_EQUAL(&(aggregator->partner_system), &(port->partner_oper.system)) &&
		     (aggregator->partner_system_priority == port->partner_oper.system_priority) &&
		     (aggregator->partner_oper_aggregator_key == port->partner_oper.key)
		    ) &&
		    ((!MAC_ADDRESS_EQUAL(&(port->partner_oper.system), &(null_mac_addr)) && /* partner answers */
		      !aggregator->is_individual)  /* but is not individual OR */
		    )
		   ) {
			/* attach to the founded aggregator */
			port->aggregator = aggregator;

----analysis: If a proper aggregator is found, port->aggregator is assigned here.

			port->actor_port_aggregator_identifier =
				port->aggregator->aggregator_identifier;
			port->next_port_in_aggregator = aggregator->lag_ports;
			port->aggregator->num_of_ports++;
			aggregator->lag_ports = port;
			slave_dbg(bond->dev, slave->dev, "Port %d joined LAG %d (existing LAG)\n",
				  port->actor_port_number,
				  port->aggregator->aggregator_identifier);

			/* mark this port as selected */
			port->sm_vars |= AD_PORT_SELECTED;
			found = 1;

----analysis: Set found to 1 if port->aggregator is assigned.

			break;
		}
	}
	/* the port couldn't find an aggregator - attach it to a new
	 * aggregator
	 */
	if (!found) {
		if (free_aggregator) {
			/* assign port a new aggregator */
			port->aggregator = free_aggregator;

----analysis: No proper free_aggregator is found. Therefore, port->aggregator cannot be assigned here.

			port->actor_port_aggregator_identifier =
				port->aggregator->aggregator_identifier;

			/* update the new aggregator's parameters
			 * if port was responsed from the end-user
			 */
			if (port->actor_oper_port_key & AD_DUPLEX_KEY_MASKS)
				/* if port is full duplex */
				port->aggregator->is_individual = false;
			else
				port->aggregator->is_individual = true;

			port->aggregator->actor_admin_aggregator_key =
				port->actor_admin_port_key;
			port->aggregator->actor_oper_aggregator_key =
				port->actor_oper_port_key;
			port->aggregator->partner_system =
				port->partner_oper.system;
			port->aggregator->partner_system_priority =
				port->partner_oper.system_priority;
			port->aggregator->partner_oper_aggregator_key = port->partner_oper.key;
			port->aggregator->receive_state = 1;
			port->aggregator->transmit_state = 1;
			port->aggregator->lag_ports = port;
			port->aggregator->num_of_ports++;

			/* mark this port as selected */
			port->sm_vars |= AD_PORT_SELECTED;

			slave_dbg(bond->dev, port->slave->dev, "Port %d joined LAG %d (new LAG)\n",
				  port->actor_port_number,
				  port->aggregator->aggregator_identifier);
		} else {
			slave_err(bond->dev, port->slave->dev,
				  "Port %d did not find a suitable aggregator\n",
				  port->actor_port_number);

----analysis: The fault scenario goes to this branch, and port->aggregator remains NULL.

		}
	}
	/* if all aggregator's ports are READY_N == TRUE, set ready=TRUE
	 * in all aggregator's ports, else set ready=FALSE in all
	 * aggregator's ports
	 */
	__set_agg_ports_ready(port->aggregator,
			      __agg_ports_are_ready(port->aggregator));

----analysis: port->aggregator is still NULL, which causes problem.


	aggregator = __get_first_agg(port);
	ad_agg_selection_logic(aggregator, update_slave_arr);

	if (!port->aggregator->is_active)
		port->actor_oper_port_state &= ~LACP_STATE_SYNCHRONIZATION;
}


Thanks.