Subject: Re: [PATCH net-next 02/12] net: sched: flower: refactor fl_change

From: Stefano Brivio <[email-masked]>
Date: Thu, 14 Feb 2019 21:34:02 +0100

On Thu, 14 Feb 2019 09:47:02 +0200
Vlad Buslov <[email-masked]> wrote:

> As a preparation for using classifier spinlock instead of relying on
> external rtnl lock, rearrange code in fl_change. The goal is to group the
> code which changes classifier state in single block in order to allow
> following commits in this set to protect it from parallel modification with
> tp->lock. Data structures that require tp->lock protection are mask
> hashtable and filters list, and classifier handle_idr.
> 
> fl_hw_replace_filter() is a sleeping function and cannot be called while
> holding a spinlock. In order to execute all sequence of changes to shared
> classifier data structures atomically, call fl_hw_replace_filter() before
> modifying them.
> 
> Signed-off-by: Vlad Buslov <[email-masked]>
> Acked-by: Jiri Pirko <[email-masked]>
> ---
>  net/sched/cls_flower.c | 85 ++++++++++++++++++++++++++------------------------
>  1 file changed, 44 insertions(+), 41 deletions(-)
> 
> diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
> index 88d7af78ba7e..91596a6271f8 100644
> --- a/net/sched/cls_flower.c
> +++ b/net/sched/cls_flower.c
> @@ -1354,90 +1354,93 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
>  	if (err < 0)
>  		goto errout;
>  
> -	if (!handle) {
> -		handle = 1;
> -		err = idr_alloc_u32(&head->handle_idr, fnew, &handle,
> -				    INT_MAX, GFP_KERNEL);
> -	} else if (!fold) {
> -		/* user specifies a handle and it doesn't exist */
> -		err = idr_alloc_u32(&head->handle_idr, fnew, &handle,
> -				    handle, GFP_KERNEL);
> -	}
> -	if (err)
> -		goto errout;
> -	fnew->handle = handle;
> -
>
> [...]
>
>  	if (fold) {
> +		fnew->handle = handle;

I'm probably missing something, but what if fold is passed and the
handle isn't specified? That can still happen, right? In that case we
wouldn't be allocating the handle.

> +
> +		err = rhashtable_insert_fast(&fnew->mask->ht, &fnew->ht_node,
> +					     fnew->mask->filter_ht_params);
> +		if (err)
> +			goto errout_hw;
> +
>  		rhashtable_remove_fast(&fold->mask->ht,
>  				       &fold->ht_node,
>  				       fold->mask->filter_ht_params);
> -		if (!tc_skip_hw(fold->flags))
> -			fl_hw_destroy_filter(tp, fold, NULL);
> -	}
> -
> -	*arg = fnew;
> -
> -	if (fold) {
>  		idr_replace(&head->handle_idr, fnew, fnew->handle);
>  		list_replace_rcu(&fold->list, &fnew->list);
> +
> +		if (!tc_skip_hw(fold->flags))
> +			fl_hw_destroy_filter(tp, fold, NULL);
>  		tcf_unbind_filter(tp, &fold->res);
>  		tcf_exts_get_net(&fold->exts);
>  		tcf_queue_work(&fold->rwork, fl_destroy_filter_work);
>  	} else {
> +		if (__fl_lookup(fnew->mask, &fnew->mkey)) {
> +			err = -EEXIST;
> +			goto errout_hw;
> +		}
> +
> +		if (handle) {
> +			/* user specifies a handle and it doesn't exist */
> +			err = idr_alloc_u32(&head->handle_idr, fnew, &handle,
> +					    handle, GFP_ATOMIC);
> +		} else {
> +			handle = 1;
> +			err = idr_alloc_u32(&head->handle_idr, fnew, &handle,
> +					    INT_MAX, GFP_ATOMIC);
> +		}
> +		if (err)
> +			goto errout_hw;

Just if you respin: a newline here would be nice to have.

> +		fnew->handle = handle;
> +
> +		err = rhashtable_insert_fast(&fnew->mask->ht, &fnew->ht_node,
> +					     fnew->mask->filter_ht_params);
> +		if (err)
> +			goto errout_idr;
> +
>  		list_add_tail_rcu(&fnew->list, &fnew->mask->filters);
>  	}
>  
> +	*arg = fnew;
> +
>  	kfree(tb);
>  	kfree(mask);
>  	return 0;
>  
> -errout_mask_ht:
> -	rhashtable_remove_fast(&fnew->mask->ht, &fnew->ht_node,
> -			       fnew->mask->filter_ht_params);
> -
> -errout_mask:
> -	fl_mask_put(head, fnew->mask, false);
> -
>  errout_idr:
>  	if (!fold)

This check could go away, I guess (not a strong preference though).

>  		idr_remove(&head->handle_idr, fnew->handle);
> +errout_hw:
> +	if (!tc_skip_hw(fnew->flags))
> +		fl_hw_destroy_filter(tp, fnew, NULL);
> +errout_mask:
> +	fl_mask_put(head, fnew->mask, false);
>  errout:
>  	tcf_exts_destroy(&fnew->exts);
>  	kfree(fnew);

-- 
Stefano