linux-kernel - Re: [PATCH v4 1/4] bpf: Make the bpf_prog_array

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Date:	Fri, 31 Jul 2015 08:46:08 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	xiakaixu <xiakaixu@...wei.com>
Cc:	Daniel Borkmann <daniel@...earbox.net>, davem@...emloft.net,
	acme@...nel.org, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	masami.hiramatsu.pt@...achi.com, jolsa@...nel.org,
	wangnan0@...wei.com, linux-kernel@...r.kernel.org,
	pi3orama@....com, hekuang@...wei.com
Subject: Re: [PATCH v4 1/4] bpf: Make the bpf_prog_array_map more generic

On 7/31/15 1:50 AM, xiakaixu wrote:
> 于 2015/7/30 9:44, Alexei Starovoitov 写道:
>> On 7/29/15 4:17 PM, Daniel Borkmann wrote:
>>>> -    if (map->map_type == BPF_MAP_TYPE_PROG_ARRAY)
>>>> +    if (map->map_type >= BPF_MAP_TYPE_PROG_ARRAY)
>>>>            /* prog_array stores refcnt-ed bpf_prog pointers
>>>>             * release them all when user space closes prog_array_fd
>>>>             */
>>>> -        bpf_prog_array_map_clear(map);
>>>> +        bpf_fd_array_map_clear(map);
>>>
>>> When we are going to add a new map type to the eBPF framework that is not
>>> an fd_array_map thing, this assumption of map->map_type >=
>>> BPF_MAP_TYPE_PROG_ARRAY
>>> might not hold then ...
>>
>> Also I think here changing == to >= is probably unnecessary.
>> prog_array needs to do it because of circular dependency
>> whereas perf_event_array cannot have it.
>> Even when we attach bpf prog to perf_event and then add it to
>> perf_event_array used by the same prog, right?
>> Please test such scenario just in case.
>
> Not sure completely understand what you mean. You know, we can
> attach bpf_prog to kprobe events. For now, we limit few event
> types, only PERF_EVENT_RAW & PERF_EVENT_HARDWARE event can
> be accessed in bpf_perf_event_read(). Seems like the dependency
> scenario won't happen.

ahh, yes, you're correct. There is no circular dependency.

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