netdev - Re: [PATCH v3 bpf-next 1/6] bpf: Create BPF_PROG_CGROUP_INET_EGRESS_RUN

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Date:   Tue, 28 May 2019 06:42:51 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     brakmo <brakmo@...com>, netdev <netdev@...r.kernel.org>
Cc:     Martin Lau <kafai@...com>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 1/6] bpf: Create
 BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY



On 5/27/19 8:49 PM, brakmo wrote:
> Create new macro BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY() to be used by
> __cgroup_bpf_run_filter_skb for EGRESS BPF progs so BPF programs can
> request cwr for TCP packets.
> 

...

> +#define BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY(array, ctx, func)		\
> +	({						\
> +		struct bpf_prog_array_item *_item;	\
> +		struct bpf_prog *_prog;			\
> +		struct bpf_prog_array *_array;		\
> +		u32 ret;				\
> +		u32 _ret = 1;				\
> +		u32 _cn = 0;				\
> +		preempt_disable();			\
> +		rcu_read_lock();			\
> +		_array = rcu_dereference(array);	\

Why _array can not be NULL here ?

> +		_item = &_array->items[0];		\
> +		while ((_prog = READ_ONCE(_item->prog))) {		\
> +			bpf_cgroup_storage_set(_item->cgroup_storage);	\
> +			ret = func(_prog, ctx);		\
> +			_ret &= (ret & 1);		\
> +			_cn |= (ret & 2);		\
> +			_item++;			\
> +		}					\
> +		rcu_read_unlock();			\
> +		preempt_enable_no_resched();	

Why are you using preempt_enable_no_resched() here ?

	\
> +		if (_ret)				\
> +			_ret = (_cn ? NET_XMIT_CN : NET_XMIT_SUCCESS);	\
> +		else					\
> +			_ret = (_cn ? NET_XMIT_DROP : -EPERM);		\
> +		_ret;					\
> +	})
> +
>  #define BPF_PROG_RUN_ARRAY(array, ctx, func)		\
>  	__BPF_PROG_RUN_ARRAY(array, ctx, func, false)
>  
>