Re: [PATCH 6/7] smp/hotplug: Differentiate the AP-work lockdep class between up and down

[Byungchul Park]

On Wed, Sep 20, 2017 at 07:00:20PM +0200, Peter Zijlstra wrote:
> With lockdep-crossrelease we get deadlock reports that span cpu-up and
> cpu-down chains. Such deadlocks cannot possibly happen because cpu-up
> and cpu-down are globally serialized.
> 
>   CPU0                  CPU1                    CPU2
>   cpuhp_up_callbacks:   takedown_cpu:           cpuhp_thread_fun:
> 
>   cpuhp_state
>                         irq_lock_sparse()
>     irq_lock_sparse()
>                         wait_for_completion()
>                                                 cpuhp_state
>                                                 complete()
> 
> Now that we have consistent AP state, we can trivially separate the
> AP-work class between up and down using st->bringup.

Could you tell me what branch you worked the patches based on?
This is similar to the problem of workqueue so I want to fix it on
top of yours, as well.

> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  kernel/cpu.c |   41 ++++++++++++++++++++++++++++++++---------
>  1 file changed, 32 insertions(+), 9 deletions(-)
> 
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -68,9 +68,26 @@ struct cpuhp_cpu_state {
>  static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);
>  
>  #if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
> -static struct lock_class_key cpuhp_state_key;
> -static struct lockdep_map cpuhp_state_lock_map =
> -	STATIC_LOCKDEP_MAP_INIT("cpuhp_state", &cpuhp_state_key);
> +static struct lockdep_map cpuhp_state_up_map =
> +	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
> +static struct lockdep_map cpuhp_state_down_map =
> +	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);
> +
> +
> +static void inline cpuhp_lock_acquire(bool bringup)
> +{
> +	lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
> +}
> +
> +static void inline cpuhp_lock_release(bool bringup)
> +{
> +	lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
> +}
> +#else
> +
> +static void inline cpuhp_lock_acquire(bool bringup) { }
> +static void inline cpuhp_lock_release(bool bringup) { }
> +
>  #endif
>  
>  /**
> @@ -512,7 +529,7 @@ static void cpuhp_thread_fun(unsigned in
>  	if (WARN_ON_ONCE(!st->should_run))
>  		return;
>  
> -	lock_map_acquire(&cpuhp_state_lock_map);
> +	cpuhp_lock_acquire(bringup);
>  
>  	if (st->single) {
>  		state = st->cb_state;
> @@ -564,7 +581,7 @@ static void cpuhp_thread_fun(unsigned in
>  	}
>  
>  next:
> -	lock_map_release(&cpuhp_state_lock_map);
> +	cpuhp_lock_release(bringup);
>  
>  	if (!st->should_run)
>  		complete(&st->done);
> @@ -581,8 +598,11 @@ cpuhp_invoke_ap_callback(int cpu, enum c
>  	if (!cpu_online(cpu))
>  		return 0;
>  
> -	lock_map_acquire(&cpuhp_state_lock_map);
> -	lock_map_release(&cpuhp_state_lock_map);
> +	cpuhp_lock_acquire(false);
> +	cpuhp_lock_release(false);
> +
> +	cpuhp_lock_acquire(true);
> +	cpuhp_lock_release(true);
>  
>  	/*
>  	 * If we are up and running, use the hotplug thread. For early calls
> @@ -620,8 +640,11 @@ static int cpuhp_kick_ap_work(unsigned i
>  	enum cpuhp_state prev_state = st->state;
>  	int ret;
>  
> -	lock_map_acquire(&cpuhp_state_lock_map);
> -	lock_map_release(&cpuhp_state_lock_map);
> +	cpuhp_lock_acquire(false);
> +	cpuhp_lock_release(false);
> +
> +	cpuhp_lock_acquire(true);
> +	cpuhp_lock_release(true);
>  
>  	trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
>  	ret = cpuhp_kick_ap(st, st->target);
>