netdev - Re: [PATCH net-next 1/8] bpf: multi program support for cgroup+bpf

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Date:   Mon, 2 Oct 2017 20:54:57 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     Daniel Borkmann <daniel@...earbox.net>, Tejun Heo <tj@...nel.org>,
        netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH net-next 1/8] bpf: multi program support for cgroup+bpf

On 10/2/17 4:48 PM, Alexei Starovoitov wrote:
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 546113430049..70f679a94804 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -27,129 +27,361 @@ void cgroup_bpf_put(struct cgroup *cgrp)
>  {
>  	unsigned int type;
>  
> -	for (type = 0; type < ARRAY_SIZE(cgrp->bpf.prog); type++) {
> -		struct bpf_prog *prog = cgrp->bpf.prog[type];
> -
> -		if (prog) {
> -			bpf_prog_put(prog);
> +	for (type = 0; type < ARRAY_SIZE(cgrp->bpf.progs); type++) {
> +		struct list_head *progs = &cgrp->bpf.progs[type];
> +		struct bpf_prog_list *pl, *tmp;
> +
> +		list_for_each_entry_safe(pl, tmp, progs, node) {
> +			list_del(&pl->node);
> +			bpf_prog_put(pl->prog);
> +			kfree(pl);
>  			static_branch_dec(&cgroup_bpf_enabled_key);
>  		}
> +		bpf_prog_array_free(cgrp->bpf.effective[type]);
> +	}
> +}
> +

...

>  
> -	if (prog)
> -		static_branch_inc(&cgroup_bpf_enabled_key);
> +	/* all allocations were successful. Activate all prog arrays */
> +	css_for_each_descendant_pre(css, &cgrp->self) {
> +		struct cgroup *desc = container_of(css, struct cgroup, self);
>  
> +		activate_effective_progs(desc, type, desc->bpf.inactive);
> +		desc->bpf.inactive = NULL;
> +	}
> +
> +	static_branch_inc(&cgroup_bpf_enabled_key);
>  	if (old_prog) {
>  		bpf_prog_put(old_prog);
>  		static_branch_dec(&cgroup_bpf_enabled_key);
>  	}
>  	return 0;

It's not clear to me that the static_branch_inc and static_branch_dec's
are equal since the dec is in the loop over each program in the list,
but the inc is not in a loop.