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

jin yiting
2021-04-20T03:22:53Z

在 2021/4/16 12:28, Jay Vosburgh 写道:
> jinyiting <jinyiting@huawei.com> wrote:
>
>> From: jin yiting <jinyiting@huawei.com>
>>
>> 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@huawei.com>
>> ---
>> 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@canonical.com
> .
>

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) {