Re: question about bonding mode 4

[Jay Vosburgh <jay.vosburgh@canonical.com>]

moyufeng <moyufeng@huawei.com> wrote:

>Ping...
>Any comments? Thanks!
>
>On 2021/1/15 10:02, moyufeng wrote:
>> 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

	Are you running the above in a script, and can you share the
entire thing?

	Does the issue occur with the current net-next?

>> 4. Repeat the preceding steps for a long time.

	When you run this test, what are the network interfaces eth0 and
eth1 connected to, and are those ports configured for VLAN 2001 and
LACP?

>> 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?

	Well, in principle, this shouldn't ever happen.  Every port
structure contains an aggregator structure, so there should always be
one available somewhere.  I'm going to speculate that there's a race
condition somewhere in the teardown processing vs the LACP state machine
that invalidates this presumption.

>> The detailed code analysis is as follows:

[...]

>> 	/* 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;

	Correct, if the "did not find a suitable aggregator" path is
taken, port->aggregator is NULL and bad things happen in the above
block.

	This is something that needs to be fixed, but I'm also concerned
that there are other issues lurking, so I'd like to be able to reproduce
this.

	-J

---
	-Jay Vosburgh, jay.vosburgh@canonical.com