Re: perf top -p broken for multithreaded processes since 5.19 #forregzbot

[Thorsten Leemhuis]

On 04.09.22 12:15, Thorsten Leemhuis wrote:
> TWIMC: this mail is primarily send for documentation purposes and for
> regzbot, my Linux kernel regression tracking bot. These mails usually
> contain '#forregzbot' in the subject, to make them easy to spot and filter.
> 
> [...]
> On 02.09.22 16:46, Tomáš Trnka wrote:
>>
>> A bug in perf v5.19 and newer completely breaks monitoring multithreaded
>> processes using "perf top -p". The tool fails to start with "Failed to mmap
>> with 22 (Invalid argument)". It still seems to work fine on single-threaded
>> processes. "perf record" is also unaffected.
>>
>> I have bisected the issue to the following commit:
>>
>> commit ae4f8ae16a07896403c90305d4b9be27f657c1fc
>> Author: Adrian Hunter <adrian.hunter@xxxxxxxxx>
>> Date:   Tue May 24 10:54:31 2022 +0300
>>
>>     libperf evlist: Allow mixing per-thread and per-cpu mmaps
>>     
>>     mmap_per_evsel() will skip events that do not match the CPU, so all CPUs
>>     can be iterated in any case.
>>
>> The issue can be easily reproduced using the following test:
>>
>> $ python - <<EOF
>> import time
>> import threading
>> th = threading.Thread(target=time.sleep, args=(3600,))
>> th.start()
>> th.join()
>> EOF
>>
>> stracing "perf top -p $(pgrep python)" yields this:
>>
>> 145184 perf_event_open({type=PERF_TYPE_HARDWARE, size=PERF_ATTR_SIZE_VER7, config=PERF_COUNT_HW_CPU_CYCLES, sample_freq=4000, sample_type=PERF_SAMPLE_IP|PERF_SAMPLE_TID|PERF_SAMPLE_TIME|PERF_SAMPLE_PERIOD, read_format=PERF_FORMAT_ID, disabled=1, exclude_kernel=1, mmap=1, comm=1, freq=1, task=1, precise_ip=0 /* arbitrary skid */, sample_id_all=1, mmap2=1, comm_exec=1, ksymbol=1, ...}, 92061, -1, -1, PERF_FLAG_FD_CLOEXEC) = 3
>>  > tools/perf/perf(evsel__open_cpu+0x287) [0x4c8ad7]
>>  > tools/perf/perf(cmd_top+0x1996) [0x439b26]
>>  > tools/perf/perf(run_builtin+0x68) [0x4a91f8]
>>  > tools/perf/perf(main+0x645) [0x40cad5]
>> 145184 perf_event_open({type=PERF_TYPE_HARDWARE, size=PERF_ATTR_SIZE_VER7, config=PERF_COUNT_HW_CPU_CYCLES, sample_freq=4000, sample_type=PERF_SAMPLE_IP|PERF_SAMPLE_TID|PERF_SAMPLE_TIME|PERF_SAMPLE_PERIOD, read_format=PERF_FORMAT_ID, disabled=1, exclude_kernel=1, mmap=1, comm=1, freq=1, task=1, precise_ip=0 /* arbitrary skid */, sample_id_all=1, mmap2=1, comm_exec=1, ksymbol=1, ...}, 104619, -1, -1, PERF_FLAG_FD_CLOEXEC) = 5
>>  > tools/perf/perf(evsel__open_cpu+0x287) [0x4c8ad7]
>>  > tools/perf/perf(cmd_top+0x1996) [0x439b26]
>>  > tools/perf/perf(run_builtin+0x68) [0x4a91f8]
>>  > tools/perf/perf(main+0x645) [0x40cad5]
>> …(snip)…
>> 145184 ioctl(5, PERF_EVENT_IOC_SET_OUTPUT, 3) = -1 EINVAL (Invalid argument)
>>  > tools/perf/perf(perf_evlist__mmap_ops+0x2cf) [0x5d497f]
>>  > tools/perf/perf(evlist__mmap+0xa7) [0x4c09b7]
>>  > perf/perf(cmd_top+0x1ccd) [0x439e5d]
>>  > tools/perf/perf(run_builtin+0x68) [0x4a91f8]
>>  > tools/perf/perf(main+0x645) [0x40cad5]
>>
>> Best regards,
>>
>> Tomáš
>> --
>> Tomáš Trnka
>> Software for Chemistry & Materials B.V.
> 
> Thanks for the report. To be sure below issue doesn't fall through the
> cracks unnoticed, I'm adding it to regzbot, my Linux kernel regression
> tracking bot:
> 
> #regzbot introduced ae4f8ae16a07896 ^
> https://bugzilla.kernel.org/show_bug.cgi?id=216441
> #regzbot title perf: perf top -p broken for multithreaded processes
> since 5.19
> #regzbot ignore-activity

#regzbot fixed-by: 7864d8f7c088aad988c44c631f1ceed9179cf2cf