If a Kernel Panic Occurs Due to a BMC Restart Analysis

Yes, your conclusion is very plausible — the kernel crash you observed appears to be directly linked to the BMC (or BMI, likely a typo for BMC) restarting, especially given the presence of USB-related stalls and a subsequent RCU stall. Here’s a breakdown of what’s happening:

🧠 Understanding the Crash

🔹 Key Indicators in Your Logs

  1. RCU Preempt Stall

    • The kernel’s RCU (Read-Copy-Update) subsystem timed out waiting for grace periods to complete. This happens when some CPUs/tasks are unable to make forward progress.
    • In your case, the rcu_preempt kthread was starved for ~10 minutes (59518 jiffies ~ 9.9 minutes assuming HZ=1000), which is extreme.

  2. CPU 1 Idling

    • An NMI (non-maskable interrupt) was sent to CPU 1, which was found in intel_idle_irq, meaning it was deep in a C-state and unresponsive to softirqs.

  3. Kworker Blocked on USB

    • The kernel thread kworker/1:1 was blocked in usb_start_wait_urb() → usb_control_msg() → usbnet_cdc_update_filter().
    • This strongly suggests a USB management/network interface (CDC-ETHER class) stopped responding.

  4. Kernel Panic

    • Triggered by RCU Stall, which is often a symptom of a broader system stall, not the root cause.

🔌 How the BMC Reboot Can Trigger This

Modern servers often expose USB devices to the host via the BMC, for purposes like:

  • Virtual KVM
  • Virtual media (USB mass storage over IPMI)
  • Management NICs exposed as USB CDC Ethernet devices (like usbnet/cdc_ether)

When the BMC resets, these virtual USB devices disappear temporarily, possibly without proper detachment, which leads to:

  • URBs (USB Request Blocks) being sent to a non-responsive USB controller
  • usbnet and kworker threads waiting indefinitely for completions that will never arrive
  • RCU threads not progressing due to blocked workers or softirq starvation
  • CPU stuck in idle C-state, not handling softirqs → leads to RCU panic

This is consistent with your backtrace, where:

  • kworker/1:1 is stuck in usbnet_cdc_update_filter(), waiting on usb_control_msg()
  • USB timeouts do not always cleanly abort, especially if underlying hardware interface is suddenly gone (e.g. BMC USB detach)

✅ Conclusion

Yes, a BMC reboot in your system configuration can very realistically:

  • Remove/disable a virtual USB device
  • Cause kernel threads using that USB (e.g. usbnet) to block indefinitely
  • Trigger an RCU stall due to downstream starvation and softirq failures
  • Lead to a kernel panic

🛠️ Recommendations

1. Mitigate USB Dependency on BMC

  • Avoid using BMC-exposed virtual USB devices in critical host kernel operations (e.g. networking).
  • If possible, use physical interfaces instead of USB CDC-based virtual ones for system management.

2. Harden USB Stack

  • Set USB URB timeouts explicitly and conservatively (usb_control_msg() has a timeout argument).
  • Apply kernel patches related to usbnet and cdc_ether robustness if available (especially for EL8 kernels).

3. Update Kernel & BMC Firmware

  • This is a known issue on older kernels (you are on 4.18.0-372.32.1.rt7.189.el8_6), where USB URB handling is brittle.
  • BMC firmware upgrades can improve hotplug detection and stability.

4. Monitor with NMI Watchdog

  • Enable NMI watchdog (nmi_watchdog=1) if not already active to capture CPU lockups earlier.

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