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Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load

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Hi Salvatore,

yesterday, I installed the kernel 5.6.0 from the Buster Backports and 
saw again a kworker process with high CPU load.
Oddly, this morning, my laptop didn't boot, so I decided to do a fresh 
install of Debian Buster 10.5.0 (image with non-free firmware because of 
my wifi card) and installed only thunderbird and vim. There is still one 
kworker process with permanently high CPU load.

I gave the dyndbg command that you told me as a kernel parameter upon 
booting and have appended the dmesg output as file dmesg.txt.gz.

Cheers,

Dirk.

Am 11.08.20 um 21:21 schrieb Salvatore Bonaccorso:
> Hi Dirk,
>
> On Tue, Aug 11, 2020 at 12:58:15PM +0200, Dirk Kostrewa wrote:
>> Hi Salavatore,
>>
>> as an additional control, I have completely uninstalled the nvidia graphics
>> driver and repeated the kworker observations using the nouveau graphics
>> driver with the kernel 4.19.0-10-amd64. This time, there are even two
>> kworker processes constantly running with high CPU load:
>>
>> $ top
>> top - 12:37:20 up 10 min,  4 users,  load average: 2.79, 2.54, 1.56
>> Tasks: 197 total,   3 running, 194 sleeping,   0 stopped,   0 zombie
>> %Cpu(s):  0.0 us, 24.2 sy,  0.0 ni, 74.2 id,  0.0 wa, 0.0 hi,  1.6 si,  0.0
>> st
>> MiB Mem :  15889.4 total,  13964.7 free,    626.8 used, 1297.9 buff/cache
>> MiB Swap:      0.0 total,      0.0 free,      0.0 used. 14849.1 avail Mem
>>
>>    PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
>>    164 root      20   0       0      0      0 R  80.0 0.0   8:41.67
>> kworker/6:2+pm
>>    455 root      20   0       0      0      0 R  80.0 0.0   8:28.23
>> kworker/2:2+pm
>>     22 root      20   0       0      0      0 S  20.0 0.0   2:14.82
>> ksoftirqd/2
>>     42 root      20   0       0      0      0 S  20.0 0.0   2:08.67
>> ksoftirqd/6
>>      1 root      20   0  169644  10212   7796 S   0.0 0.1   0:01.52 systemd
>>      2 root      20   0       0      0      0 S   0.0 0.0   0:00.00 kthreadd
>>      3 root       0 -20       0      0      0 I   0.0 0.0   0:00.00 rcu_gp
>>      4 root       0 -20       0      0      0 I   0.0 0.0   0:00.00
>> rcu_par_gp
>>      6 root       0 -20       0      0      0 I   0.0 0.0   0:00.00
>> kworker/0:0H-kblockd
>>      7 root      20   0       0      0      0 I   0.0 0.0   0:00.05
>> kworker/u16:0-event+
>>
>> The stacks of the two kworker processes show the same output:
>>
>> [<0>] 0xffffffffffffffff
>>
>> I have appended the top 5000 lines tracing as a compressed ascii file
>> out-cut.txt,gz and the dmesg output as compressed ascii file dmesg.txt.gz.
>>
>> I hope, this helps to find out where the problem with the high CPU load of
>> the kworker processes come from.
> Thanks this is very helpful.
>
> I suspect what you are seeing is an issue with the usb hubport present
> before but now uncovered due to the upstream change e9fb08d617bf
> ("xhci: prevent bus suspend if a roothub port detected a over-current
> condition")[1], which was as well backported to v4.19.y in 4.19.119.
>
> Can you add some dynamic debugging on the 'drivers/usb/'[2] ideally at
> boot time. On runtime it is
>
> # echo 'file drivers/usb/* +p;' > /sys/kernel/debug/dynamic_debug/control
>
> or as kernel parameter to have enable the debug messages at boot time
> already:
>
> dyndbg="file drivers/usb/* +p;"
>
> Can you attach the dmesg with the enabled debugging?
>
> Regards,
> Salvatore
>
>   [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e9fb08d617bfae5471d902112667d0eeb9dee3c4
>   [2] https://www.kernel.org/doc/html/latest/admin-guide/dynamic-debug-howto.html

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Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Salvatore Bonaccorso <carnil@debian.org> - 2020-08-02 15:50 +0200
  Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Salvatore Bonaccorso <carnil@debian.org> - 2020-08-02 18:30 +0200
    Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Salvatore Bonaccorso <carnil@debian.org> - 2020-08-11 21:30 +0200
      Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Dirk Kostrewa <dirk.kostrewa@mailbox.org> - 2020-08-12 13:10 +0200
        Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Dirk Kostrewa <dirk.kostrewa@mailbox.org> - 2020-08-12 18:00 +0200
          Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Salvatore Bonaccorso <carnil@debian.org> - 2020-08-12 18:10 +0200
            Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Dirk Kostrewa <dirk.kostrewa@mailbox.org> - 2020-08-13 11:00 +0200
            Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Dirk Kostrewa <dirk.kostrewa@mailbox.org> - 2020-08-21 11:40 +0200
          Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Salvatore Bonaccorso <carnil@debian.org> - 2020-08-28 16:40 +0200
            Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Salvatore Bonaccorso <carnil@debian.org> - 2020-08-29 11:40 +0200
              Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Dirk Kostrewa <dirk.kostrewa@mailbox.org> - 2020-09-04 18:00 +0200
                Bug#966703: linux-image-4.19.0-10-amd64: kworker process with permanent high CPU load Salvatore Bonaccorso <carnil@debian.org> - 2020-09-04 19:20 +0200

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