Re: [PATCH net v3 2/2] bonding: 802.3ad: fix no transmission of LACPDUs

[Jonathan Toppins]

On 8/16/22 09:41, Jonathan Toppins wrote:
> On 8/16/22 09:11, Jay Vosburgh wrote:
> > Jonathan Toppins <jtoppins@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > >
> > > 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