Hello Nysal,
On 25/10/25 13:35, Nysal Jan K.A. wrote:
If SMT is disabled or a partial SMT state is enabled, when a new kernel image is loaded for kexec, on reboot the following warning is observed:
kexec: Waking offline cpu 228. WARNING: CPU: 0 PID: 9062 at arch/powerpc/kexec/core_64.c:223 kexec_prepare_cpus+0x1b0/0x1bc [snip] NIP kexec_prepare_cpus+0x1b0/0x1bc LR kexec_prepare_cpus+0x1a0/0x1bc Call Trace: kexec_prepare_cpus+0x1a0/0x1bc (unreliable) default_machine_kexec+0x160/0x19c machine_kexec+0x80/0x88 kernel_kexec+0xd0/0x118 __do_sys_reboot+0x210/0x2c4 system_call_exception+0x124/0x320 system_call_vectored_common+0x15c/0x2ec
This occurs as add_cpu() fails due to cpu_bootable() returning false for CPUs that fail the cpu_smt_thread_allowed() check or non primary threads if SMT is disabled.
Fix the issue by enabling SMT and resetting the number of SMT threads to the number of threads per core, before attempting to wake up all present CPUs.
Fixes: 38253464bc82 ("cpu/SMT: Create topology_smt_thread_allowed()") Reported-by: Sachin P Bappalige sachinpb@linux.ibm.com Cc: stable@vger.kernel.org # v6.6+ Signed-off-by: Nysal Jan K.A. nysal@linux.ibm.com
arch/powerpc/kexec/core_64.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c index 222aa326dace..ff6df43720c4 100644 --- a/arch/powerpc/kexec/core_64.c +++ b/arch/powerpc/kexec/core_64.c @@ -216,6 +216,11 @@ static void wake_offline_cpus(void) { int cpu = 0;
- lock_device_hotplug();
- cpu_smt_num_threads = threads_per_core;
- cpu_smt_control = CPU_SMT_ENABLED;
Above variables are #define if CONFIG_SMP and CONFIG_HOTPLUG_SMT is not there.
I think the above code should go under #if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT).
Seems like the build failure reported below is also pointing the same issue: https://lore.kernel.org/all/202510280824.Fe2D1Sbw-lkp@intel.com/
- unlock_device_hotplug();
- for_each_present_cpu(cpu) { if (!cpu_online(cpu)) { printk(KERN_INFO "kexec: Waking offline cpu %d.\n",