Subject: Re: [PATCH] bonding: 3ad: Fix the conflict between bond_update_slave_arr and the state machine

From: Jay Vosburgh <[email-masked]>
Date: Mon, 26 Apr 2021 08:22:37 -0700

David Miller <[email-masked]> wrote:

>From: jinyiting <[email-masked]>
>Date: Wed, 21 Apr 2021 16:38:21 +0800
>
>> 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.
>> 
>> The conflict occurred 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.
>> 
>> Also, bond_update_slave_arr is normal for potential sleep when
>> allocating memory, so replace the WARN_ON with a call to might_sleep.
>> 
>> Signed-off-by: jinyiting <[email-masked]>
>> ---
>> 
>> Previous versions:
>>  * https://lore.kernel.org/netdev/[email-masked]/
>> 
>>  drivers/net/bonding/bond_main.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>> index 74cbbb2..83ef62d 100644
>> --- a/drivers/net/bonding/bond_main.c
>> +++ b/drivers/net/bonding/bond_main.c
>> @@ -4406,7 +4404,9 @@ 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);
>
>The code paths that call this function with mode_lock held will now deadlock.

	No path should be calling bond_update_slave_arr with mode_lock
already held (it expects RTNL only); did you find one?

	My concern is that there's something else that does the opposite
order, i.e., mode_lock first, then RTNL, but I haven't found an example.

	-J

---
	-Jay Vosburgh, [email-masked]