Subject: Re: [net-next 5/9] net/mlx5e: Implement CT entry update

From: Vlad Buslov <[email-masked]>
Date: Thu, 16 Feb 2023 19:15:13 +0200

On Thu 16 Feb 2023 at 16:51, Maciej Fijalkowski <[email-masked]> wrote:
> On Wed, Feb 15, 2023 at 04:09:14PM -0800, Saeed Mahameed wrote:
>> From: Vlad Buslov <[email-masked]>
>> 
>> With support for UDP NEW offload the flow_table may now send updates for
>> existing flows. Support properly replacing existing entries by updating
>> flow restore_cookie and replacing the rule with new one with the same match
>> but new mod_hdr action that sets updated ctinfo.
>> 
>> Signed-off-by: Vlad Buslov <[email-masked]>
>> Reviewed-by: Oz Shlomo <[email-masked]>
>> Reviewed-by: Paul Blakey <[email-masked]>
>> Signed-off-by: Saeed Mahameed <[email-masked]>
>> ---
>>  .../ethernet/mellanox/mlx5/core/en/tc_ct.c    | 118 +++++++++++++++++-
>>  1 file changed, 117 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c b/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c
>> index 193562c14c44..76e86f83b6ac 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c
>> @@ -871,6 +871,68 @@ mlx5_tc_ct_entry_add_rule(struct mlx5_tc_ct_priv *ct_priv,
>>  	return err;
>>  }
>>  
>> +static int
>> +mlx5_tc_ct_entry_replace_rule(struct mlx5_tc_ct_priv *ct_priv,
>> +			      struct flow_rule *flow_rule,
>> +			      struct mlx5_ct_entry *entry,
>> +			      bool nat, u8 zone_restore_id)
>> +{
>> +	struct mlx5_ct_zone_rule *zone_rule = &entry->zone_rules[nat];
>> +	struct mlx5_flow_attr *attr = zone_rule->attr, *old_attr;
>> +	struct mlx5e_mod_hdr_handle *mh;
>> +	struct mlx5_ct_fs_rule *rule;
>> +	struct mlx5_flow_spec *spec;
>> +	int err;
>> +
>> +	spec = kvzalloc(sizeof(*spec), GFP_KERNEL);
>> +	if (!spec)
>> +		return -ENOMEM;
>> +
>> +	old_attr = mlx5_alloc_flow_attr(ct_priv->ns_type);
>> +	if (!attr) {
>
> when can attr == NULL? maybe check it in the first place before allocing
> spec above?

Should verify 'old_attr', not 'attr'. Thanks for catching this!

>
>> +		err = -ENOMEM;
>> +		goto err_attr;
>> +	}
>> +	*old_attr = *attr;
>> +
>> +	err = mlx5_tc_ct_entry_create_mod_hdr(ct_priv, attr, flow_rule, &mh, zone_restore_id,
>> +					      nat, mlx5_tc_ct_entry_has_nat(entry));
>> +	if (err) {
>> +		ct_dbg("Failed to create ct entry mod hdr");
>> +		goto err_mod_hdr;
>> +	}
>> +
>> +	mlx5_tc_ct_set_tuple_match(ct_priv, spec, flow_rule);
>> +	mlx5e_tc_match_to_reg_match(spec, ZONE_TO_REG, entry->tuple.zone, MLX5_CT_ZONE_MASK);
>> +
>> +	rule = ct_priv->fs_ops->ct_rule_add(ct_priv->fs, spec, attr, flow_rule);
>> +	if (IS_ERR(rule)) {
>> +		err = PTR_ERR(rule);
>> +		ct_dbg("Failed to add replacement ct entry rule, nat: %d", nat);
>> +		goto err_rule;
>> +	}
>> +
>> +	ct_priv->fs_ops->ct_rule_del(ct_priv->fs, zone_rule->rule);
>> +	zone_rule->rule = rule;
>> +	mlx5_tc_ct_entry_destroy_mod_hdr(ct_priv, old_attr, zone_rule->mh);
>> +	zone_rule->mh = mh;
>> +
>> +	kfree(old_attr);
>> +	kvfree(spec);
>
> not a big deal but you could make a common goto below with a different
> name

You mean jump from here to the middle of the error handling code below
in order not to duplicate these two calls to *free()? Honestly, I would
much rather prefer _not_ to do that since goto is necessary evil for
error handling in C but I don't believe we should handle any common
non-error code paths with it and it is not typically done in mlx5.

>
>> +	ct_dbg("Replaced ct entry rule in zone %d", entry->tuple.zone);
>> +
>> +	return 0;
>> +
>> +err_rule:
>> +	mlx5_tc_ct_entry_destroy_mod_hdr(ct_priv, zone_rule->attr, mh);
>> +	mlx5_put_label_mapping(ct_priv, attr->ct_attr.ct_labels_id);
>> +err_mod_hdr:
>> +	kfree(old_attr);
>> +err_attr:
>> +	kvfree(spec);
>> +	return err;
>> +}
>> +
>>  static bool
>>  mlx5_tc_ct_entry_valid(struct mlx5_ct_entry *entry)
>>  {
>> @@ -1065,6 +1127,52 @@ mlx5_tc_ct_entry_add_rules(struct mlx5_tc_ct_priv *ct_priv,
>>  	return err;
>>  }
>>  
>> +static int
>> +mlx5_tc_ct_entry_replace_rules(struct mlx5_tc_ct_priv *ct_priv,
>> +			       struct flow_rule *flow_rule,
>> +			       struct mlx5_ct_entry *entry,
>> +			       u8 zone_restore_id)
>> +{
>> +	int err;
>> +
>> +	err = mlx5_tc_ct_entry_replace_rule(ct_priv, flow_rule, entry, false,
>
> would it make sense to replace the bool nat in here with some kind of
> enum?

It is either nat rule or non-nat rule. Why would we invent an enum here?
Moreover, boolean 'nat' is already used in multiple places in this file,
so this patch just re-uses existing convention.

>
>> +					    zone_restore_id);
>> +	if (err)
>> +		return err;
>> +
>> +	err = mlx5_tc_ct_entry_replace_rule(ct_priv, flow_rule, entry, true,
>> +					    zone_restore_id);
>> +	if (err)
>> +		mlx5_tc_ct_entry_del_rule(ct_priv, entry, false);
>> +	return err;
>> +}
>> +
>> +static int
>> +mlx5_tc_ct_block_flow_offload_replace(struct mlx5_ct_ft *ft, struct flow_rule *flow_rule,
>> +				      struct mlx5_ct_entry *entry, unsigned long cookie)
>> +{
>> +	struct mlx5_tc_ct_priv *ct_priv = ft->ct_priv;
>> +	int err;
>> +
>> +	err = mlx5_tc_ct_entry_replace_rules(ct_priv, flow_rule, entry, ft->zone_restore_id);
>> +	if (!err)
>> +		return 0;
>> +
>> +	/* If failed to update the entry, then look it up again under ht_lock
>> +	 * protection and properly delete it.
>> +	 */
>> +	spin_lock_bh(&ct_priv->ht_lock);
>> +	entry = rhashtable_lookup_fast(&ft->ct_entries_ht, &cookie, cts_ht_params);
>> +	if (entry) {
>> +		rhashtable_remove_fast(&ft->ct_entries_ht, &entry->node, cts_ht_params);
>> +		spin_unlock_bh(&ct_priv->ht_lock);
>> +		mlx5_tc_ct_entry_put(entry);
>> +	} else {
>> +		spin_unlock_bh(&ct_priv->ht_lock);
>> +	}
>> +	return err;
>> +}
>> +
>>  static int
>>  mlx5_tc_ct_block_flow_offload_add(struct mlx5_ct_ft *ft,
>>  				  struct flow_cls_offload *flow)
>> @@ -1087,9 +1195,17 @@ mlx5_tc_ct_block_flow_offload_add(struct mlx5_ct_ft *ft,
>>  	spin_lock_bh(&ct_priv->ht_lock);
>>  	entry = rhashtable_lookup_fast(&ft->ct_entries_ht, &cookie, cts_ht_params);
>>  	if (entry && refcount_inc_not_zero(&entry->refcnt)) {
>> +		if (entry->restore_cookie == meta_action->ct_metadata.cookie) {
>> +			spin_unlock_bh(&ct_priv->ht_lock);
>> +			mlx5_tc_ct_entry_put(entry);
>> +			return -EEXIST;
>> +		}
>> +		entry->restore_cookie = meta_action->ct_metadata.cookie;
>>  		spin_unlock_bh(&ct_priv->ht_lock);
>> +
>> +		err = mlx5_tc_ct_block_flow_offload_replace(ft, flow_rule, entry, cookie);
>>  		mlx5_tc_ct_entry_put(entry);
>
> in case of err != 0, haven't you already put the entry inside
> mlx5_tc_ct_block_flow_offload_replace() ?

No. Here we release the reference that was obtained 10 lines up and
mlx5_tc_ct_block_flow_offload_replace() releases the reference held by
ct_entries_ht table.

>
>> -		return -EEXIST;
>> +		return err;
>>  	}
>>  	spin_unlock_bh(&ct_priv->ht_lock);
>>  
>> -- 
>> 2.39.1
>>