Re: [tip: locking/core] lockdep: Fix lockdep recursion

[Peter Zijlstra]

On Thu, Oct 15, 2020 at 11:49:26AM +0200, Peter Zijlstra wrote:
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1764,8 +1764,7 @@ static bool rcu_gp_init(void)
>  		smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values.
>  		firstseq = READ_ONCE(rnp->ofl_seq);
>  		if (firstseq & 0x1)
> -			while (firstseq == smp_load_acquire(&rnp->ofl_seq))
> -				schedule_timeout_idle(1);  // Can't wake unless RCU is watching.
> +			smp_cond_load_relaxed(&rnp->ofl_seq, VAL == firstseq);

My bad, that should be: VAL != firstseq.

>  		smp_mb(); // Pair with barriers used when updating ->ofl_seq to even values.
>  		raw_spin_lock(&rcu_state.ofl_lock);
>  		raw_spin_lock_irq_rcu_node(rnp);