Multiple kernel errors for "serial8250: too much work for irq4" are reported in log messages

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 7
    • Kernel version older than kernel-3.10.0-1160.el7
  • Red Hat Enterprise Linux 8
    • Kernel versions older than kernel-4.18.0-305.el8
  • Microsoft Hyper-V (Version: 7.0) / KVM

Issue

  • Following error is reported in /var/log/messages in Hyper-V or KVM guest.

    "serial8250: too much work for irq4"

Resolution

  • For Red Hat Enterprise Linux 7: this issue has been resolved with kernel-3.10.0-1160.el7 or later via RHSA-2020:4060.

  • For Red Hat Enterprise Linux 8: this issue has been resolved with kernel-4.18.0-305.el8 or later via RHSA-2021:1578.

Root Cause

  • The too much work for irq4 message is intended as an informational message, not to describe a problem with the serial console port (COM1) itself.
  • It might have a performance problem with the emulated COM1 in the VM with high vCPU counts. The occurrence of this message may be an indication of some other underlying problem that is delaying the output of messages to COM1. Diagnostic efforts should focus on finding and resolving the underlying problem.

  • Below commit will resolve issue:

    commit 9d7c249a1ef9bf0d5696df14e6bc067004f16979
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date:   Thu Aug 2 13:14:32 2018 +0200

    serial: 8250: drop the printk from serial8250_interrupt()

Diagnostic Steps

  • Check for the presence of serial8250: too much work for irq4 in /var/log/messages or the output of the journalctl or dmesg commands.

    # dmesg | grep -i serial
[  755.621087] serial8250: too much work for irq4
[  778.890023] serial8250: too much work for irq4
[  796.898017] serial8250: too much work for irq4

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