netdev - Re: [PATCH v2 net-next] bpf: fix bpf_perf_event

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Message-ID: <5629065C.6020103@plumgrid.com>
Date:	Thu, 22 Oct 2015 08:53:00 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>, Wang Nan <wangnan0@...wei.com>,
	He Kuang <hekuang@...wei.com>, Kaixu Xia <xiakaixu@...wei.com>,
	Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next] bpf: fix bpf_perf_event_read() helper

On 10/22/15 6:57 AM, Peter Zijlstra wrote:
> On Wed, Oct 21, 2015 at 03:58:03PM -0700, Alexei Starovoitov wrote:
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 64754bfecd70..0b6333265872 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -3258,7 +3258,7 @@ static inline u64 perf_event_count(struct perf_event *event)
>>   u64 perf_event_read_local(struct perf_event *event)
>>   {
>>   	unsigned long flags;
>> -	u64 val;
>> +	u64 val = -EINVAL;
>
> No, you cannot do this, -EINVAL is a valid count value. You simply must
> not call this function on !local events, ever.

agree. Will keep perf_event_read_local() as-is and do all safety
checks on bpf side.


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