6.12-stable review patch. If anyone has any objections, please let me know.
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From: Nysal Jan K.A. nysal@linux.ibm.com
commit c2296a1e42418556efbeb5636c4fa6aa6106713a upstream.
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+ Reviewed-by: Srikar Dronamraju srikar@linux.ibm.com Signed-off-by: Nysal Jan K.A. nysal@linux.ibm.com Tested-by: Samir M samir@linux.ibm.com Reviewed-by: Sourabh Jain sourabhjain@linux.ibm.com Signed-off-by: Madhavan Srinivasan maddy@linux.ibm.com Link: https://patch.msgid.link/20251028105516.26258-1-nysal@linux.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kexec/core_64.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
--- a/arch/powerpc/kexec/core_64.c +++ b/arch/powerpc/kexec/core_64.c @@ -202,6 +202,23 @@ static void kexec_prepare_cpus_wait(int mb(); }
+ +/* + * The add_cpu() call in wake_offline_cpus() can fail as cpu_bootable() + * returns false for CPUs that fail the cpu_smt_thread_allowed() check + * or non primary threads if SMT is disabled. Re-enable SMT and set the + * number of SMT threads to threads per core. + */ +static void kexec_smt_reenable(void) +{ +#if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT) + lock_device_hotplug(); + cpu_smt_num_threads = threads_per_core; + cpu_smt_control = CPU_SMT_ENABLED; + unlock_device_hotplug(); +#endif +} + /* * We need to make sure each present CPU is online. The next kernel will scan * the device tree and assume primary threads are online and query secondary @@ -216,6 +233,8 @@ static void wake_offline_cpus(void) { int cpu = 0;
+ kexec_smt_reenable(); + for_each_present_cpu(cpu) { if (!cpu_online(cpu)) { printk(KERN_INFO "kexec: Waking offline cpu %d.\n",