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SubjectRe: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability
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On 07.04.2020 19:36, Arnaldo Carvalho de Melo wrote:
> Em Tue, Apr 07, 2020 at 05:54:27PM +0300, Alexey Budankov escreveu:
>> On 07.04.2020 17:35, Arnaldo Carvalho de Melo wrote:
>>> Em Tue, Apr 07, 2020 at 11:30:14AM -0300, Arnaldo Carvalho de Melo escreveu:
>>>> [perf@five ~]$ type perf
<SNIP>
>>>> perf is hashed (/home/perf/bin/perf)
>>>> [perf@five ~]$
>>>
>>> Humm, perf record falls back to cycles:u after initially trying cycles
>>> (i.e. kernel and userspace), lemme see trying 'perf top -e cycles:u',
>>> lemme test, humm not really:
>>>
>>> [perf@five ~]$ perf top --stdio -e cycles:u
>>> Error:
>>> Failed to mmap with 1 (Operation not permitted)
>>> [perf@five ~]$ perf record -e cycles:u -a sleep 1
>>> [ perf record: Woken up 1 times to write data ]
>>> [ perf record: Captured and wrote 1.123 MB perf.data (132 samples) ]
>>> [perf@five ~]$
>>>
>>> Back to debugging this.
>>
>> Could makes sense adding cap_ipc_lock to the binary to isolate from this:
>>
>> kernel/events/core.c: 6101
>> if ((locked > lock_limit) && perf_is_paranoid() &&
>> !capable(CAP_IPC_LOCK)) {
>> ret = -EPERM;
>> goto unlock;
>> }
>
>
> That did the trick, I'll update the documentation and include in my
> "Committer testing" section:

Looks like top mode somehow reaches perf mmap limit described here [1].
Using -m option solves the issue avoiding cap_ipc_lock on my 8 cores machine:
perf top -e cycles -m 1

~Alexey

[1] https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html#memory-allocation

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