On Wed, Oct 28, 2020 at 02:27:42PM -0400, Qian Cai wrote: > The call to rcu_cpu_starting() in smp_init_secondary() is not early > enough in the CPU-hotplug onlining process, which results in lockdep > splats as follows: > > WARNING: suspicious RCU usage > ----------------------------- > kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!! > > other info that might help us debug this: > > RCU used illegally from offline CPU! > rcu_scheduler_active = 1, debug_locks = 1 > no locks held by swapper/1/0. > > Call Trace: > show_stack+0x158/0x1f0 > dump_stack+0x1f2/0x238 > __lock_acquire+0x2640/0x4dd0 > lock_acquire+0x3a8/0xd08 > _raw_spin_lock_irqsave+0xc0/0xf0 > clockevents_register_device+0xa8/0x528 > init_cpu_timer+0x33e/0x468 > smp_init_secondary+0x11a/0x328 > smp_start_secondary+0x82/0x88 > > This is avoided by moving the call to rcu_cpu_starting up near the > beginning of the smp_init_secondary() function. Note that the > raw_smp_processor_id() is required in order to avoid calling into > lockdep before RCU has declared the CPU to be watched for readers. > > Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/ > Signed-off-by: Qian Cai <cai@xxxxxxxxxx> Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > --- > arch/s390/kernel/smp.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c > index ebfe86d097f0..390d97daa2b3 100644 > --- a/arch/s390/kernel/smp.c > +++ b/arch/s390/kernel/smp.c > @@ -855,13 +855,14 @@ void __init smp_detect_cpus(void) > > static void smp_init_secondary(void) > { > - int cpu = smp_processor_id(); > + int cpu = raw_smp_processor_id(); > > S390_lowcore.last_update_clock = get_tod_clock(); > restore_access_regs(S390_lowcore.access_regs_save_area); > set_cpu_flag(CIF_ASCE_PRIMARY); > set_cpu_flag(CIF_ASCE_SECONDARY); > cpu_init(); > + rcu_cpu_starting(cpu); > preempt_disable(); > init_cpu_timer(); > vtime_init(); > -- > 2.28.0 >
