Qian Cai <c...@redhat.com> writes: > The call to rcu_cpu_starting() in start_secondary() is not early enough > in the CPU-hotplug onlining process, which results in lockdep splats as > follows:
Since when? What kernel version? I haven't seen this running CPU hotplug tests with PROVE_LOCKING=y on v5.10-rc1. Am I missing a CONFIG? cheers > 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: > dump_stack+0xec/0x144 (unreliable) > lockdep_rcu_suspicious+0x128/0x14c > __lock_acquire+0x1060/0x1c60 > lock_acquire+0x140/0x5f0 > _raw_spin_lock_irqsave+0x64/0xb0 > clockevents_register_device+0x74/0x270 > register_decrementer_clockevent+0x94/0x110 > start_secondary+0x134/0x800 > start_secondary_prolog+0x10/0x14 > > This is avoided by moving the call to rcu_cpu_starting up near the > beginning of the start_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 <c...@redhat.com> > --- > arch/powerpc/kernel/smp.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c > index 3c6b9822f978..8c2857cbd960 100644 > --- a/arch/powerpc/kernel/smp.c > +++ b/arch/powerpc/kernel/smp.c > @@ -1393,13 +1393,14 @@ static void add_cpu_to_masks(int cpu) > /* Activate a secondary processor. */ > void start_secondary(void *unused) > { > - unsigned int cpu = smp_processor_id(); > + unsigned int cpu = raw_smp_processor_id(); > > mmgrab(&init_mm); > current->active_mm = &init_mm; > > smp_store_cpu_info(cpu); > set_dec(tb_ticks_per_jiffy); > + rcu_cpu_starting(cpu); > preempt_disable(); > cpu_callin_map[cpu] = 1; > > -- > 2.28.0
