Re: [PATCH] bonding: 3ad: update slave arr after initialize

[jin yiting]

在 2021/4/16 12:28, Jay Vosburgh 写道:
> jinyiting <jinyiting@xxxxxxxxxx> wrote:
>
> > From: jin yiting <jinyiting@xxxxxxxxxx>
> >
> > The bond works in mode 4, and performs down/up operations on the bond
> > that is normally negotiated. The probability of bond-> slave_arr is NULL
> >
> > Test commands:
> >     ifconfig bond1 down
> >     ifconfig bond1 up
> >
> > The conflict occurs in the following process：
> >
> > __dev_open (CPU A)
> > --bond_open
> >    --queue_delayed_work(bond->wq,&bond->ad_work,0);
> >    --bond_update_slave_arr
> >      --bond_3ad_get_active_agg_info
> >
> > ad_work(CPU B)
> > --bond_3ad_state_machine_handler
> >    --ad_agg_selection_logic
> >
> > ad_work runs on cpu B. In the function ad_agg_selection_logic, all
> > agg->is_active will be cleared. Before the new active aggregator is
> > selected on CPU B, bond_3ad_get_active_agg_info failed on CPU A,
> > bond->slave_arr will be set to NULL. The best aggregator in
> > ad_agg_selection_logic has not changed, no need to update slave arr.
> >
> > Signed-off-by: jin yiting <jinyiting@xxxxxxxxxx>
> > ---
> > drivers/net/bonding/bond_3ad.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
> > index 6908822..d100079 100644
> > --- a/drivers/net/bonding/bond_3ad.c
> > +++ b/drivers/net/bonding/bond_3ad.c
> > @@ -2327,6 +2327,12 @@ void bond_3ad_state_machine_handler(struct work_struct *work)
> >
> > 			aggregator = __get_first_agg(port);
> > 			ad_agg_selection_logic(aggregator, &update_slave_arr);
> > +			if (!update_slave_arr) {
> > +				struct aggregator *active = __get_active_agg(aggregator);
> > +
> > +				if (active && active->is_active)
> > +					update_slave_arr = true;
> > +			}
> > 		}
> > 		bond_3ad_set_carrier(bond);
> > 	}
>
> 	The described issue is a race condition (in that
> ad_agg_selection_logic clears agg->is_active under mode_lock, but
> bond_open -> bond_update_slave_arr is inspecting agg->is_active outside
> the lock).  I don't see how the above change will reliably manage this;
> the real issue looks to be that bond_update_slave_arr is committing
> changes to the array (via bond_reset_slave_arr) based on a racy
> inspection of the active aggregator state while it is in flux.
>
> 	Also, the description of the issue says "The best aggregator in
> ad_agg_selection_logic has not changed, no need to update slave arr,"
> but the change above does the opposite, and will set update_slave_arr
> when the aggregator has not changed (update_slave_arr remains false at
> return of ad_agg_selection_logic).
>
> 	I believe I understand the described problem, but I don't see
> how the patch fixes it.  I suspect (but haven't tested) that the proper
> fix is to acquire mode_lock in bond_update_slave_arr while calling
> bond_3ad_get_active_agg_info to avoid conflict with the state machine.
>
> 	-J
>
> ---
> 	-Jay Vosburgh, jay.vosburgh@xxxxxxxxxxxxx
> .

	Thank you for your reply. The last patch does have redundant update 
slave arr.Thank you for your correction.

        As you said, holding mode_lock in bond_update_slave_arr while 
calling bond_3ad_get_active_agg_info can avoid conflictwith the state 
machine. I have tested this patch, with ifdown/ifup operations for bond 
or slaves.

        But bond_update_slave_arr is expected to hold RTNL only and NO 
other lock. And it have WARN_ON(lockdep_is_held(&bond->mode_lock)); in 
bond_update_slave_arr. I'm not sure that holding mode_lock in 
bond_update_slave_arr while calling bond_3ad_get_active_agg_info is a 
correct action.


diff --git a/drivers/net/bonding/bond_main.c 
b/drivers/net/bonding/bond_main.c
index 74cbbb2..db988e5 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -4406,7 +4406,9 @@ int bond_update_slave_arr(struct bonding *bond, 
struct slave *skipslave)
    if (BOND_MODE(bond) == BOND_MODE_8023AD) {
        struct ad_info ad_info;

+       spin_lock_bh(&bond->mode_lock);
        if (bond_3ad_get_active_agg_info(bond, &ad_info)) {
+           spin_unlock_bh(&bond->mode_lock);
            pr_debug("bond_3ad_get_active_agg_info failed\n");
            /* No active aggragator means it's not safe to use
             * the previous array.
@@ -4414,6 +4416,7 @@ int bond_update_slave_arr(struct bonding *bond, 
struct slave *skipslave)
            bond_reset_slave_arr(bond);
            goto out;
        }
+       spin_unlock_bh(&bond->mode_lock);
        agg_id = ad_info.aggregator_id;
    }
    bond_for_each_slave(bond, slave, iter) {