CM5/Pi5: CPU hotplug broken - CPU_ON fails after CPU_OFF (PSCI)
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 42/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Quiet
- Tech stack
- c, linux, raspberry-pi
- Domain
- embedded-iot, operating-systems
Research direction
Start by reproducing the failure with /sys/devices/system/cpu/cpu1/online and capture the dmesg messages shown. Read the kernel's PSCI CPU_OFF and CPU_ON handling and the CPU hotplug path, then compare behavior after a cold boot and kexec. Done means CPU1 can be taken offline and brought online again without -22, including in the reported kexec case.
Written by the indexing model from the issue text.
Description
Describe the bug
Description:
- After taking a CPU offline via /sys/devices/system/cpu/cpuN/online
- Bringing it back online fails with error -22
- dmesg shows: "psci: failed to boot CPU1 (-22)"
- Same failure occurs after kexec when target kernel tries CPU_ON
- Only cold boot resets the PSCI state machine
Impact:
- CPU hotplug is non-functional
- kexec to new kernel fails to bring up secondary CPUs
Hardware: Raspberry Pi CM5
Steps to reproduce the behaviour
on root shell, do:
echo 0>/sys/devices/system/cpu/cpu1/online
echo 1>/sys/devices/system/cpu/cpu1/online
Device (s)
Raspberry Pi CM5 Lite
System
(! 518)-> cat /etc/rpi-issue
Raspberry Pi reference 2025-12-04
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 4997bf4e4e49bc3305eb182a4a08bd023529da04, stage4
(! 519)-> vcgencmd version
2025/12/08 19:29:54
Copyright (c) 2012 Broadcom
version 2226a853 (release) (embedded)
(! 520)-> uname -a
Linux scorscion 6.12.75+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.12.75-1+rpt1 (2026-03-11) aarch64 GNU/Linux
Logs
[ 1654.502987] psci: CPU1 killed (polled 0 ms)
[ 1677.441585] CPU1: failed to come online
[ 1677.445450] CPU1: failed in unknown state : 0x0
[ 1772.549796] psci: failed to boot CPU1 (-22)
[ 1772.549806] CPU1: failed to boot: -22
Additional context
No response
- Dominant language
- C
- Stars
- 13.2k
- Forks
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- Avg merge
- 2d 21h
- Merged PRs (30d)
- 21
Contributor guide
No contributing guide indexed for this repository
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
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