On Sat, 2020-10-31 at 19:37 +0100, Heiko Carstens wrote: > 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> > > --- > > arch/s390/kernel/smp.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > Could you provide the config you used? I'm wondering why I can't > reproduce this even though I have lot's of debug options enabled. https://cailca.coding.net/public/linux/mm/git/files/master/s390.config Essentially, I believe it requires CONFIG_PROVE_RCU_LIST=y. Also, it occurs to me that this only starts to happen after the commit mentioned in the above link.
