Message-ID: <3d76f4c3-916a-9abe-745f-e2781fad1b24@redhat.com>
Date:   Tue, 16 Aug 2022 13:47:07 -0400
From:   Jonathan Toppins <jtoppins@...hat.com>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     netdev@...r.kernel.org, liuhangbin@...il.com,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v3 2/2] bonding: 802.3ad: fix no transmission of
 LACPDUs

On 8/16/22 09:41, Jonathan Toppins wrote:
> On 8/16/22 09:11, Jay Vosburgh wrote:
>> Jonathan Toppins <jtoppins@...hat.com> wrote:
>>
>>> This is caused by the global variable ad_ticks_per_sec being zero as
>>> demonstrated by the reproducer script discussed below. This causes
>>> all timer values in __ad_timer_to_ticks to be zero, resulting
>>> in the periodic timer to never fire.
>>>
>>> To reproduce:
>>> Run the script in
>>> `tools/testing/selftests/drivers/net/bonding/bond-break-lacpdu-tx.sh` 
>>> which
>>> puts bonding into a state where it never transmits LACPDUs.
>>>
>>> line 44: ip link add fbond type bond mode 4 miimon 200 \
>>>             xmit_hash_policy 1 ad_actor_sys_prio 65535 lacp_rate fast
>>> setting bond param: ad_actor_sys_prio
>>> given:
>>>     params.ad_actor_system = 0
>>> call stack:
>>>     bond_option_ad_actor_sys_prio()
>>>     -> bond_3ad_update_ad_actor_settings()
>>>        -> set ad.system.sys_priority = bond->params.ad_actor_sys_prio
>>>        -> ad.system.sys_mac_addr = bond->dev->dev_addr; because
>>>             params.ad_actor_system == 0
>>> results:
>>>      ad.system.sys_mac_addr = bond->dev->dev_addr
>>>
>>> line 48: ip link set fbond address 52:54:00:3B:7C:A6
>>> setting bond MAC addr
>>> call stack:
>>>     bond->dev->dev_addr = new_mac
>>>
>>> line 52: ip link set fbond type bond ad_actor_sys_prio 65535
>>> setting bond param: ad_actor_sys_prio
>>> given:
>>>     params.ad_actor_system = 0
>>> call stack:
>>>     bond_option_ad_actor_sys_prio()
>>>     -> bond_3ad_update_ad_actor_settings()
>>>        -> set ad.system.sys_priority = bond->params.ad_actor_sys_prio
>>>        -> ad.system.sys_mac_addr = bond->dev->dev_addr; because
>>>             params.ad_actor_system == 0
>>> results:
>>>      ad.system.sys_mac_addr = bond->dev->dev_addr
>>>
>>> line 60: ip link set veth1-bond down master fbond
>>> given:
>>>     params.ad_actor_system = 0
>>>     params.mode = BOND_MODE_8023AD
>>>     ad.system.sys_mac_addr == bond->dev->dev_addr
>>> call stack:
>>>     bond_enslave
>>>     -> bond_3ad_initialize(); because first slave
>>>        -> if ad.system.sys_mac_addr != bond->dev->dev_addr
>>>           return
>>> results:
>>>      Nothing is run in bond_3ad_initialize() because dev_add equals
>>>      sys_mac_addr leaving the global ad_ticks_per_sec zero as it is
>>>      never initialized anywhere else.
>>>
>>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>>> Signed-off-by: Jonathan Toppins <jtoppins@...hat.com>
>>> ---
>>>
>>> Notes:
>>>     v2:
>>>      * split this fix from the reproducer
>>>     v3:
>>>      * rebased to latest net/master
>>>
>>> drivers/net/bonding/bond_3ad.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/bonding/bond_3ad.c 
>>> b/drivers/net/bonding/bond_3ad.c
>>> index d7fb33c078e8..957d30db6f95 100644
>>> --- a/drivers/net/bonding/bond_3ad.c
>>> +++ b/drivers/net/bonding/bond_3ad.c
>>> @@ -84,7 +84,8 @@ enum ad_link_speed_type {
>>> static const u8 null_mac_addr[ETH_ALEN + 2] __long_aligned = {
>>>     0, 0, 0, 0, 0, 0
>>> };
>>> -static u16 ad_ticks_per_sec;
>>> +
>>> +static u16 ad_ticks_per_sec = 1000 / AD_TIMER_INTERVAL;
>>> static const int ad_delta_in_ticks = (AD_TIMER_INTERVAL * HZ) / 1000;
>>
>>     I still feel like this is kind of a hack, as it's not really
>> fixing bond_3ad_initialize to actually work (which is the real problem
>> as I understand it).  If it's ok to skip all that for this case, then
>> why do we ever need to call bond_3ad_initialize?
>>
> 
> The way it is currently written you still need to call 
> bond_3ad_initialize() just not for setting the tick resolution. The 
> issue here is ad_ticks_per_sec is used in several places to calculate 
> timer periods, __ad_timer_to_ticks(), for various timers in the 802.3ad 
> protocol. And if this variable, ad_ticks_per_sec, is left uninitialized 
> all of these timer periods go to zero. Since the value passed in 
> bond_3ad_initialize() is an immediate value I simply moved it off of the 
> call stack and set the static global variable instead.
> 
> To fix bond_3ad_initialize(), probably something like the below is 
> needed, but I do not understand why the guard if check was placed in 
> bond_3ad_initialize().

I looked at the history of the if guard in bond_3ad_initialize and it 
has existed since the creation of the git tree. It appears since commit 
5ee14e6d336f ("bonding: 3ad: apply ad_actor settings changes 
immediately") the if guard is no longer needed and removing the if guard 
would also fix the problem, I have not tested yet.

I think this patch series can be accepted as-is because, it does fix the 
issue as demonstrated by the kselftest accompanying the series and is 
the smallest change to fix the issue.

Further, I don't see why we want to set the file-scoped variable, 
ad_ticks_per_sec, inside bond_3ad_initialize() as ad_ticks_per_sec is 
utilized across all bonds. It seems like ad_ticks_per_sec should be 
changed to a const and set at the top of the file. I see no value in 
passing the value as an unnamed constant on the stack when 
bond_3ad_initialize is called. These changes however could be done in 
the net-next tree as follow-on cleanup patches.

Jay, how would you like to proceed?

[...]

Thanks,
-Jon

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