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

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Message-ID: <55BB36C9.4050007@huawei.com>
Date:	Fri, 31 Jul 2015 16:50:17 +0800
From:	xiakaixu <xiakaixu@...wei.com>
To:	Alexei Starovoitov <ast@...mgrid.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

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.
I will add the event decrement refcnt function to map_free in V5.
right?
> 
> 
> .
> 


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