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Date:   Sun, 8 Mar 2020 10:15:00 +0200
From:   Paul Blakey <paulb@...lanox.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Oz Shlomo <ozsh@...lanox.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...lanox.com>, Roi Dayan <roid@...lanox.com>
Subject: Re: [PATCH net-next v6 1/3] net/sched: act_ct: Create nf flow table
 per zone

On 3/8/2020 10:11 AM, Paul Blakey wrote:

> iirc I did the spin lock bh because we can be called from queue work rcu handler , so I wanted to disable soft irq.
>
> I got a possible deadlock splat for that.

Here I meant this call rcu:

static void tcf_ct_cleanup(struct tc_action *a)
{
>-------struct tcf_ct_params *params;
>-------struct tcf_ct *c = to_ct(a);

>-------params = rcu_dereference_protected(c->params, 1);
>-------if (params)
>------->-------call_rcu(&params->rcu, tcf_ct_params_free);
}

static void tcf_ct_params_free(struct rcu_head *head)
{
>-------struct tcf_ct_params *params = container_of(head,
>------->------->------->------->------->-------    struct tcf_ct_params, rcu);

>-------tcf_ct_flow_table_put(params);

...


>
>
> On 3/7/2020 10:53 PM, Eric Dumazet wrote:
>
>> On 3/7/20 12:12 PM, Eric Dumazet wrote:
>>> On 3/3/20 7:57 AM, Paul Blakey wrote:
>>>> Use the NF flow tables infrastructure for CT offload.
>>>>
>>>> Create a nf flow table per zone.
>>>>
>>>> Next patches will add FT entries to this table, and do
>>>> the software offload.
>>>>
>>>> Signed-off-by: Paul Blakey <paulb@...lanox.com>
>>>> Reviewed-by: Jiri Pirko <jiri@...lanox.com>
>>>> ---
>>>>   v4->v5:
>>>>     Added reviewed by Jiri, thanks!
>>>>   v3->v4:
>>>>     Alloc GFP_ATOMIC
>>>>   v2->v3:
>>>>     Ditch re-locking to alloc, and use atomic allocation
>>>>   v1->v2:
>>>>     Use spin_lock_bh instead of spin_lock, and unlock for alloc (as it can sleep)
>>>>     Free ft on last tc act instance instead of last instance + last offloaded tuple,
>>>>     this removes cleanup cb and netfilter patches, and is simpler
>>>>     Removed accidental mlx5/core/en_tc.c change
>>>>     Removed reviewed by Jiri - patch changed
>>>>
>>>> +	err = nf_flow_table_init(&ct_ft->nf_ft);
>>> This call is going to allocate a rhashtable (GFP_KERNEL allocations that might sleep)
>>>
>>> Since you still hold zones_lock spinlock, a splat should occur.
>>>
>>> "BUG: sleeping function called from invalid context in  ..."
>>>
>>> DEBUG_ATOMIC_SLEEP=y is your friend.
>>>
>>> And it is always a good thing to make sure a patch does not trigger a lockdep splat
>>>
>>> CONFIG_PROVE_LOCKING=y
>> Also abusing a spinlock and GFP_ATOMIC allocations in control path is highly discouraged.
>>
>> I can not test the following fix, any objections before I submit this officially ?
>>
>> diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
>> index 23eba61f0f819212a3522c3c63b938d0b8d997e2..3d9e678d7d5336f1746035745b091bea0dcb5fdd 100644
>> --- a/net/sched/act_ct.c
>> +++ b/net/sched/act_ct.c
>> @@ -35,15 +35,15 @@
>>  
>>  static struct workqueue_struct *act_ct_wq;
>>  static struct rhashtable zones_ht;
>> -static DEFINE_SPINLOCK(zones_lock);
>> +static DEFINE_MUTEX(zones_mutex);
>>  
>>  struct tcf_ct_flow_table {
>>         struct rhash_head node; /* In zones tables */
>>  
>>         struct rcu_work rwork;
>>         struct nf_flowtable nf_ft;
>> +       refcount_t ref;
>>         u16 zone;
>> -       u32 ref;
>>  
>>         bool dying;
>>  };
>> @@ -64,14 +64,15 @@ static int tcf_ct_flow_table_get(struct tcf_ct_params *params)
>>         struct tcf_ct_flow_table *ct_ft;
>>         int err = -ENOMEM;
>>  
>> -       spin_lock_bh(&zones_lock);
>> +       mutex_lock(&zones_mutex);
>>         ct_ft = rhashtable_lookup_fast(&zones_ht, &params->zone, zones_params);
>> -       if (ct_ft)
>> -               goto take_ref;
>> +       if (ct_ft && refcount_inc_not_zero(&ct_ft->ref))
>> +               goto out_unlock;
>>  
>> -       ct_ft = kzalloc(sizeof(*ct_ft), GFP_ATOMIC);
>> +       ct_ft = kzalloc(sizeof(*ct_ft), GFP_KERNEL);
>>         if (!ct_ft)
>>                 goto err_alloc;
>> +       refcount_set(&ct_ft->ref, 1);
>>  
>>         ct_ft->zone = params->zone;
>>         err = rhashtable_insert_fast(&zones_ht, &ct_ft->node, zones_params);
>> @@ -84,10 +85,9 @@ static int tcf_ct_flow_table_get(struct tcf_ct_params *params)
>>                 goto err_init;
>>  
>>         __module_get(THIS_MODULE);
>> -take_ref:
>> +out_unlock:
>>         params->ct_ft = ct_ft;
>> -       ct_ft->ref++;
>> -       spin_unlock_bh(&zones_lock);
>> +       mutex_unlock(&zones_mutex);
>>  
>>         return 0;
>>  
>> @@ -96,7 +96,7 @@ static int tcf_ct_flow_table_get(struct tcf_ct_params *params)
>>  err_insert:
>>         kfree(ct_ft);
>>  err_alloc:
>> -       spin_unlock_bh(&zones_lock);
>> +       mutex_unlock(&zones_mutex);
>>         return err;
>>  }
>>  
>> @@ -116,13 +116,11 @@ static void tcf_ct_flow_table_put(struct tcf_ct_params *params)
>>  {
>>         struct tcf_ct_flow_table *ct_ft = params->ct_ft;
>>  
>> -       spin_lock_bh(&zones_lock);
>> -       if (--params->ct_ft->ref == 0) {
>> +       if (refcount_dec_and_test(&params->ct_ft->ref)) {
>>                 rhashtable_remove_fast(&zones_ht, &ct_ft->node, zones_params);
>>                 INIT_RCU_WORK(&ct_ft->rwork, tcf_ct_flow_table_cleanup_work);
>>                 queue_rcu_work(act_ct_wq, &ct_ft->rwork);
>>         }
>> -       spin_unlock_bh(&zones_lock);
>>  }
>>  
>>  static void tcf_ct_flow_table_add(struct tcf_ct_flow_table *ct_ft,
>>

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