Re: [PATCH] s390/smp: Move rcu_cpu_starting() earlier

[Heiko Carstens <hca@linux.ibm.com>]

On Sat, Oct 31, 2020 at 07:38:52PM -0400, Qian Cai wrote:
> > > 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@redhat.com>
> > > ---
> > >  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.

Yes, with that enabled I can reprocuce it. Thanks! It depends on
CONFIG_RCU_EXPERT. I can't image why I didn't had that enabled.. :)