linux-kernel - Re: [PATCH] s390/smp: Move rcu_cpu

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Date:   Sun, 1 Nov 2020 17:05:54 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Qian Cai <cai@...hat.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/smp: Move rcu_cpu_starting() earlier

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@...hat.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.. :)