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Date:   Mon, 20 Jul 2020 10:39:56 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     LKML <linux-kernel@vger.kernel.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Greg KH <gregkh@linuxfoundation.org>
Cc:     linux-usb@vger.kernel.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>
Subject: kworker/0:3+pm hogging CPU
Message-ID: <20200720083956.GA4074@dhcp22.suse.cz>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,
I am not sure when this started happening but at least 5.6, 5.7 and
5.8-rc6 all exhibit this problem. Please note that the this is happining
on a laptop which is not completely healthy. The BIOS complains that the
Battery cannot be charged because the power supply cannot be recognized.
This is somehting I have for a longer time without noticing the
kworker/0:3+pm problem so I do not think they are related but who knows.

Anyway, kworker/0:3+pm is hogging CPU. /proc/<pid>/0:3+pm is very often
empty so I suspect it just schedules very often and performs only small
amount of work. Here are few backtraces I've managed to catch

[<0>] preempt_schedule_thunk+0x16/0x18
[<0>] usb_hcd_submit_urb+0x686/0x773
[<0>] usb_start_wait_urb+0x59/0xc8
[<0>] usb_control_msg+0xd4/0x10d
[<0>] get_port_status+0x51/0x6f
[<0>] hub_port_status+0x41/0xa3
[<0>] hub_activate+0x230/0x4ee
[<0>] hub_resume+0x20/0x9a
[<0>] usb_resume_interface.isra.0+0xb0/0xd0
[<0>] usb_suspend_both+0xf6/0x20c
[<0>] usb_runtime_suspend+0x32/0x62
[<0>] __rpm_callback+0x70/0xd4
[<0>] rpm_callback+0x55/0x6b
[<0>] rpm_suspend+0x2af/0x440
[<0>] __pm_runtime_suspend+0x48/0x62
[<0>] usb_runtime_idle+0x26/0x2d
[<0>] __rpm_callback+0x70/0xd4
[<0>] rpm_idle+0x179/0x1df
[<0>] pm_runtime_work+0x6b/0x81
[<0>] process_one_work+0x1bd/0x2c6
[<0>] worker_thread+0x19c/0x240
[<0>] kthread+0x11b/0x123
[<0>] ret_from_fork+0x22/0x30

[<0>] slab_pre_alloc_hook+0x15/0x46
[<0>] __kmalloc+0x148/0x15a
[<0>] usb_hcd_submit_urb+0x5c6/0x773
[<0>] usb_start_wait_urb+0x59/0xc8
[<0>] usb_control_msg+0xd4/0x10d
[<0>] get_port_status+0x51/0x6f
[<0>] hub_port_status+0x41/0xa3
[<0>] hub_activate+0x230/0x4ee
[<0>] hub_resume+0x20/0x9a
[<0>] usb_resume_interface.isra.0+0xb0/0xd0
[<0>] usb_suspend_both+0xf6/0x20c

[<0>] slab_pre_alloc_hook+0x15/0x46
[<0>] __kmalloc+0x148/0x15a
[<0>] usb_hcd_submit_urb+0x5c6/0x773
[<0>] usb_start_wait_urb+0x59/0xc8
[<0>] usb_control_msg+0xd4/0x10d
[<0>] set_port_feature+0x33/0x38
[<0>] hub_suspend+0x15c/0x16a
[<0>] usb_suspend_both+0x91/0x20c
[<0>] usb_runtime_suspend+0x32/0x62
[<0>] __rpm_callback+0x70/0xd4
[<0>] rpm_callback+0x55/0x6b
[<0>] rpm_suspend+0x2af/0x440
[<0>] __pm_runtime_suspend+0x48/0x62
[<0>] usb_runtime_idle+0x26/0x2d
[<0>] __rpm_callback+0x70/0xd4
[<0>] rpm_idle+0x179/0x1df
[<0>] pm_runtime_work+0x6b/0x81
[<0>] process_one_work+0x1bd/0x2c6
[<0>] worker_thread+0x19c/0x240
[<0>] kthread+0x11b/0x123
[<0>] ret_from_fork+0x22/0x30

Is this something known or something I can give more information about?
From a very quick look into the code it sounds as if the system wanted
to suspend an USB device/controller but that keeps failing again and
again.
-- 
Michal Hocko
SUSE Labs