Subject: Re: Bond recovery from BOND_LINK_FAIL state not working

From: Jay Vosburgh <[email-masked]>
Date: Fri, 03 Nov 2017 11:26:01 -0700

Alex Sidorenko <[email-masked]> wrote:

>Jay,
>
>while scenario you describe makes sense, it does not match what we see in our tests.
>
>The instrumentation prints info every time we enter bond_mii_monitor(), bond_miimon_inspect(),
>bond_miimon_commit() and every time we are committing link state. And we print a message every time we
>propose BOND_LINK_FAIL in bond_miimon_inspect()
>
>So in your scenario,
>
>2) bond_mii_monitor rtnl_trylock fails, it reschedules
>
>we should see bond_miimon_inspect() 'proposed BOND_LINK_FAIL' debugging message without matching
>'commit' messages. But what we see in reality is that for each 'proposed' there is 'commit' message.
>(And we don't expect ens3f1 to really go down when VC module is rebooted - it is not connected to it).
>
>Here is debugging output (with the fix I have suggested in my first email *applied*),
>my comments inline.
>
>  (FYI: in "bond_mii_monitor: ens3f0 current link state: 0" lines we print slave->link when entering bond_mii_monitor)
>
>***
>
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f0 current link state: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f1 current link state: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_UP case on slave ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_UP case on slave ens3f1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f0 current link state: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f1 current link state: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_UP case on slave ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_UP case on slave ens3f1
><snipped NetworkManager lines>
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f0 current link state: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f1 current link state: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_UP case on slave ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: proposed BOND_LINK_FAIL on slave ens3f0
>             /*FALLTHRU*/
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_FAIL case on slave ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: set new_link=BOND_LINK_DOWN on slave ens3f0
>
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_UP case on slave ens3f1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect returned non-zero
>
>   As you see in lines above, we reach BOND_LINK_FAIL on ens3f0 only, ens3f1 has good link_state and we
>   do not reach BOND_LINK_FAIL fallthru and do not propose anything
>   (otherwise there would be debugging output for it)
>
>   Now we are in bond_mii_monitor() bond_for_each_slave() loop, committing link states - and suddenly
>       we have state 0->1 for interface ens3f1 as well as for ens3f0
>
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: committing link state 0->1 for interface ens3f0, 0 Mbps full duplex
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: slave->should_notify_link for interface ens3f0 now: 1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: committing link state 0->1 for interface ens3f1, 20000 Mbps full duplex
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: slave->should_notify_link for interface ens3f1 now: 1

	Does your instrumentation show each slave's ->link_new_state at
each entry to bond_miimon_inspect?  Not just when commit, et al, is
called, but the actual value of the variable each time through the
function?  Or maybe you've got an entry for the propose way back in the
log somewhere?

	I'm wondering here whether you're seeing "step 6" from the
failure path I described, i.e., the slave->link_new_state on ens3f1 was
set some time previously (perhaps a long time) and has been silently
pending until some event happens on the other slave to trigger a commit
cycle.

	Something had to have set the variable, and from your
instrumentation, it does not appear that it was the immediately prior
instance of bond_miimon_inspect.  In net-next's bonding driver, nothing
other than the _propose call will enter BOND_LINK_FAIL state.

	-J

>   Entering bond_miimon_commit()
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: working on slave ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: BOND_LINK_DOWN
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: link status definitely down for interface ens3f0, disabling it
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_find_best_slave: slave->link: 2, up: false, slave->delay: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_find_best_slave: slave->link: 1, up: true, slave->delay: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_find_best_slave: no bestslave found, bond failure imminent
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_select_active_slave: best_slave != curr_active_slave
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_select_active_slave: best_slave is NULL, this is probably bad
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_change_active_slave: old_active: ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_change_active_slave: new_active: NULL
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: Removing MAC from old_active
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: ALB and TLB modes should call bond_alb_handle_active_change
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_set_carrier: turning carrier off
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: now running without any active interface!
>
>        Even though link state of ens3f1 has changed, we have BOND_LINK_NOCHANGE
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: working on slave ens3f1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: BOND_LINK_NOCHANGE on slave ens3f1
>
>    Another invocation of bond_mii_monitor
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f0 current link state: 2
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f1 current link state: 1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_DOWN case on slave ens3f0
>
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_FAIL case on slave ens3f1
>
>   We see "up again on ens3f1" and execute slave->new_link = BOND_LINK_UP; (my initial suggestion)
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: link status up again after 0 ms for interface ens3f1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_inspect returned non-zero
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: committing link state 2->2 for interface ens3f0, 0 Mbps full duplex
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: slave->should_notify_link for interface ens3f0 now: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: committing link state 1->0 for interface ens3f1, 20000 Mbps full duplex
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: slave->should_notify_link for interface ens3f1 now: 0
>
>   As we nudged slave->new_link, bond_miimon_commit() now works
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: working on slave ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: BOND_LINK_NOCHANGE on slave ens3f0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: working on slave ens3f1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_miimon_commit: BOND_LINK_UP
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: link status definitely up for interface ens3f1, 20000 Mbps full duplex
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_find_best_slave: slave->link: 2, up: false, slave->delay: 0
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_find_best_slave: slave ens3f1 BOND_LINK_UP
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_select_active_slave: best_slave != curr_active_slave
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_change_active_slave: old_active: NULL
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_change_active_slave: new_active: ens3f1
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: Non-BOND_LINK_BACK case
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: making interface ens3f1 the new active one
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: Setting MAC on new_active
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: ALB and TLB modes should call bond_alb_handle_active_change
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: bond_set_carrier: turning carrier on
>Oct 31 09:09:25 SYDC1LNX kernel: bond0: first active interface up!
><snipped NetworkManager lines>
>Oct 31 09:09:26 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f0 current link state: 2
>Oct 31 09:09:26 SYDC1LNX kernel: bond0: bond_mii_monitor: ens3f1 current link state: 0
>Oct 31 09:09:26 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_DOWN case on slave ens3f0
>Oct 31 09:09:26 SYDC1LNX kernel: bond0: bond_miimon_inspect: entered BOND_LINK_UP case on slave ens3f1
>...
>
>Alex
>
>On 11/02/2017 09:11 PM, Jay Vosburgh wrote:
>> Alex Sidorenko <[email-masked]> wrote:
>>> On 11/02/2017 12:51 AM, Jay Vosburgh wrote:
>>>> Jarod Wilson <[email-masked]> wrote:
>>>>
>>>>> On 2017-11-01 8:35 PM, Jay Vosburgh wrote:
>>>>>> Jay Vosburgh <[email-masked]> wrote:
>>>>>>
>>>>>>> Alex Sidorenko <[email-masked]> wrote:
>>>>>>>
>>>>>>>> The problem has been found while trying to deploy RHEL7 on HPE Synergy
>>>>>>>> platform, it is seen both in customer's environment and in HPE test lab.
>>>>>>>>
>>>>>>>> There are several bonds configured in TLB mode and miimon=100, all other
>>>>>>>> options are default. Slaves are connected to VirtualConnect
>>>>>>>> modules. Rebooting a VC module should bring one bond slave (ens3f0) down
>>>>>>>> temporarily, but not another one (ens3f1). But what we see is
>>>>>>>>
>>>>>>>> Oct 24 10:37:12 SYDC1LNX kernel: bond0: link status up again after 0 ms for interface ens3f1
>>>>>>
>>>>>> 	In net-next, I don't see a path in the code that will lead to
>>>>>> this message, as it would apparently require entering
>>>>>> bond_miimon_inspect in state BOND_LINK_FAIL but with downdelay set to 0.
>>>>>> If downdelay is 0, the code will transition to BOND_LINK_DOWN and not
>>>>>> remain in _FAIL state.
>>>>>
>>>>> The kernel in question is laden with a fair bit of additional debug spew,
>>>>> as we were going back and forth, trying to isolate where things were going
>>>>> wrong.  That was indeed from the BOND_LINK_FAIL state in
>>>>> bond_miimon_inspect, inside the if (link_state) clause though, so after
>>>>> commit++, there's a continue, which ... does what now? Doesn't it take us
>>>>> back to the top of the bond_for_each_slave_rcu() loop, so we bypass the
>>>>> next few lines of code that would have led to a transition to
>>>>> BOND_LINK_DOWN?
>>>>
>>>> 	Just to confirm: your downdelay is 0, correct?
>>>
>>> Correct.
>>>
>>>>
>>>> 	And, do you get any other log messages other than "link status
>>>> up again after 0 ms"?
>>>
>>> Yes, here are some messages (from an early instrumentation):
>> [...]
>>> That is, we never see ens3f1 going to BOND_LINK_DOWN and it continues
>>> staying in BOND_LINK_NOCHANGE/BOND_LINK_FAIL
>>>
>>>
>>>>
>>>> 	To answer your question, yes, the "if (link_state) {" block in
>>>> the BOND_LINK_FAIL case of bond_miimon_inspect ends in continue, but
>>>> this path is nominally for the downdelay logic.  If downdelay is active
>>>> and the link recovers before the delay expires, the link should never
>>>> have moved to BOND_LINK_DOWN.  The commit++ causes bond_miimon_inspect
>>>> to return nonzero, causing in turn the bond_propose_link_state change to
>>>> BOND_LINK_FAIL state to be committed.  This path deliberately does not
>>>> set slave->new_link, as downdelay is purposely delaying the transition
>>>> to BOND_LINK_DOWN.
>>>>
>>>> 	If downdelay is 0, the slave->link should not persist in
>>>> BOND_LINK_FAIL state; it should set new_link = BOND_LINK_DOWN which will
>>>> cause a transition in bond_miimon_commit.  The bond_propose_link_state
>>>> call to set BOND_LINK_FAIL in the BOND_LINK_UP case will be committed in
>>>> bond_mii_monitor prior to calling bond_miimon_commit, which will in turn
>>>> do the transition to _DOWN state.  In this case, the BOND_LINK_FAIL case
>>>> "if (link_state) {" block should never be entered.
>>>
>>> I totally agree with your description of transition logic, and this is why
>>> we were puzzled by how this can occur until we noticed NetworkManager
>>> messages around this time and decided to run a test without it.
>>> Without NM, everything works as expected. After that, adding more
>>> instrumentation, we have found that we do not propose BOND_LINK_FAIL inside
>>> bond_miimon_inspect() but elsewhere (NetworkManager?).
>>
>> 	I think I see the flaw in the logic.
>>
>> 	1) bond_miimon_inspect finds link_state = 0, then makes a call
>> to bond_propose_link_state(BOND_LINK_FAIL), setting link_new_state to
>> BOND_LINK_FAIL.  _inspect then sets slave->new_link = BOND_LINK_DOWN and
>> returns non-zero.
>>
>> 	2) bond_mii_monitor rtnl_trylock fails, it reschedules.
>>
>> 	3) bond_mii_monitor runs again, and calls bond_miimon_inspect.
>>
>> 	4) the slave's link has recovered, so link_state != 0.
>> slave->link is still BOND_LINK_UP.  The slave's link_new_state remains
>> set to BOND_LINK_FAIL, but new_link is reset to NOCHANGE.
>> bond_miimon_inspect returns 0, so nothing is committed.
>>
>> 	5) step 4 can repeat indefinitely.
>>
>> 	6) eventually, the other slave does something that causes
>> commit++, making bond_mii_monitor call bond_commit_link_state and then
>> bond_miimon_commit.  The slave in question from steps 1-4 still has
>> link_new_state as BOND_LINK_FAIL, but new_link is NOCHANGE, so it ends
>> up in BOND_LINK_FAIL state.
>>
>> 	I think step 6 could also occur concurrently with the initial
>> pass through step 4 to induce the problem.
>>
>> 	It looks like Mahesh mostly fixed this in
>>
>> commit fb9eb899a6dc663e4a2deed9af2ac28f507d0ffb
>> Author: Mahesh Bandewar <[email-masked]>
>> Date:   Tue Apr 11 22:36:00 2017 -0700
>>
>>      bonding: handle link transition from FAIL to UP correctly
>>
>> 	but the window still exists, and requires the slave link state
>> to change between the failed rtnl_trylock and the second pass through
>> _inspect.  The problem is that a state transition has been kept between
>> invocations to _inspect, but the condition that induced the transition
>> has changed.
>>
>> 	I haven't tested these, but I suspect the solution is either to
>> clear link_new_state on entry to the loop in bond_miimon_inspect, or
>> merge new_state and link_new_state as a single "next state" (which is
>> cleared on entry to the loop).
>>
>> 	The first of these is a pretty simple patch:
>>
>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>> index 18b58e1376f1..6f89f9981a6c 100644
>> --- a/drivers/net/bonding/bond_main.c
>> +++ b/drivers/net/bonding/bond_main.c
>> @@ -2046,6 +2046,7 @@ static int bond_miimon_inspect(struct bonding *bond)
>>     	bond_for_each_slave_rcu(bond, slave, iter) {
>>   		slave->new_link = BOND_LINK_NOCHANGE;
>> +		slave->link_new_state = slave->link;
>>     		link_state = bond_check_dev_link(bond, slave->dev, 0);
>>   
>>
>> 	Alex / Jarod, could you check my logic, and would you be able to
>> test this patch if my analysis appears sound?
>>
>> 	Thanks,
>>
>> 	-J
>>
>> ---
>> 	-Jay Vosburgh, [email-masked]
>>
>
>-- 
>------------------------------------------------------------------
>Alex Sidorenko	email: [email-masked]
>ERT  Linux 	Hewlett-Packard Enterprise (Canada)
>------------------------------------------------------------------