On Fri, 2020-10-09 at 13:36 -0400, Qian Cai wrote: > Back to x86, we have: > > start_secondary() > smp_callin() > apic_ap_setup() > setup_local_APIC() > printk() in certain conditions. > > which is before smp_store_cpu_info(). > > Can't we add a rcu_cpu_starting() at the very top for each start_secondary(), > secondary_start_kernel(), smp_start_secondary() etc, so we don't worry about > any printk() later? This is rather irony. rcu_cpu_starting() is taking a lock and then reports itself. [ 8.826732][ T0] __lock_acquire.cold.76+0x2ad/0x3e0 [ 8.826732][ T0] lock_acquire+0x1c8/0x820 [ 8.826732][ T0] _raw_spin_lock_irqsave+0x30/0x50 [ 8.826732][ T0] rcu_cpu_starting+0xd0/0x2c0 [ 8.826732][ T0] start_secondary+0x10/0x2a0 [ 8.826732][ T0] secondary_startup_64_no_verify+0xb8/0xbb
