Re: [PATCH v7 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat

[Joel Fernandes]

This patch submission got completely screwed up, sorry, please ignore. I'll
repost soon. There's something messed up with my SMTP server too.

On Tue, May 15, 2018 at 03:45:54PM -0700, Joel Fernandes (Google) wrote:
> I'm able to reproduce a lockdep splat with config options:
> CONFIG_PROVE_LOCKING=y,
> CONFIG_DEBUG_LOCK_ALLOC=y and
> CONFIG_PREEMPTIRQ_EVENTS=y
> 
> $ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable
> ---
>  kernel/softirq.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 177de3640c78..8a040bcaa033 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt)
>  {
>  	lockdep_assert_irqs_disabled();
>  
> +	if (preempt_count() == cnt)
> +		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
> +
>  	if (softirq_count() == (cnt & SOFTIRQ_MASK))
>  		trace_softirqs_on(_RET_IP_);
> -	preempt_count_sub(cnt);
> +
> +	__preempt_count_sub(cnt);
>  }
>  
>  /*
> -- 
> 2.17.0.441.gb46fe60e1d-goog
>