Messages in this thread | | | From | Jay Vosburgh <> | Subject | Re: [PATCH] bonding: 3ad: Fix the conflict between bond_update_slave_arr and the state machine | Date | Mon, 26 Apr 2021 12:29:22 -0700 |
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David Miller <davem@davemloft.net> wrote:
>From: Jay Vosburgh <jay.vosburgh@canonical.com> >Date: Mon, 26 Apr 2021 08:22:37 -0700 > >> David Miller <davem@davemloft.net> wrote: >> >>>From: jinyiting <jinyiting@huawei.com> >>>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 <jinyiting@huawei.com> >>>> --- >>>> >>>> Previous versions: >>>> * https://lore.kernel.org/netdev/612b5e32-ea11-428e-0c17-e2977185f045@huawei.com/ >>>> >>>> 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. >> > >This patch is removing a lockdep assertion masking sure that mode_lock was held >when this function was called. That should have been triggering all the time, right?
The line in question is:
#ifdef CONFIG_LOCKDEP WARN_ON(lockdep_is_held(&bond->mode_lock)); #endif
The WARN_ON is triggering if mode_lock is held, not asserting that mode_lock is held. I think that's wrong anyway, since mode_lock could be held by some other thread, leading to false positives, thus the change to might_sleep.
-J
--- -Jay Vosburgh, jay.vosburgh@canonical.com
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