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Subject: Re: [PATCH v2] cpu/hotplug: Do not bail-out in DYING/STARTING
 sections
To:     Vincent Donnefort <vdonnefort@google.com>, peterz@infradead.org,
        tglx@linutronix.de
Cc:     linux-kernel@vger.kernel.org, vschneid@redhat.com,
        kernel-team@android.com
References: <20220523160536.2889162-1-vdonnefort@google.com>
From:   Derek Dolney <z23@posteo.net>
Message-ID: <77d0ed9b-8521-c4a9-69c4-ec82cba81e61@posteo.net>
Date:   Thu, 26 May 2022 12:27:26 +0000
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In-Reply-To: <20220523160536.2889162-1-vdonnefort@google.com>
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Tested by: Derek Dolney <z23@posteo.net>

Suspend and resume with tboot are working again with this patch. Tested
on 5.12 broken commit and latest git 5.18.

On 5/23/22 12:05 PM, Vincent Donnefort wrote:
> The DYING/STARTING callbacks are not expected to fail. However, as reported
> by Derek, drivers such as tboot are still free to return errors within
> those sections. In that case, there's nothing the hotplug machinery can do,
> so let's just proceed and log the failures.
> 
> Fixes: 453e41085183 (cpu/hotplug: Add cpuhp_invoke_callback_range())
> Reported-by: Derek Dolney <z23@posteo.net>
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> 
> ---
> 
> v1 -> v2: 
>    - Commit message rewording.
>    - More details in the warnings.
>    - Some variable renaming
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index bbad5e375d3b..c3617683459e 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -663,21 +663,51 @@ static bool cpuhp_next_state(bool bringup,
>  	return true;
>  }
>  
> -static int cpuhp_invoke_callback_range(bool bringup,
> -				       unsigned int cpu,
> -				       struct cpuhp_cpu_state *st,
> -				       enum cpuhp_state target)
> +static int _cpuhp_invoke_callback_range(bool bringup,
> +					unsigned int cpu,
> +					struct cpuhp_cpu_state *st,
> +					enum cpuhp_state target,
> +					bool nofail)
>  {
>  	enum cpuhp_state state;
> -	int err = 0;
> +	int ret = 0;
>  
>  	while (cpuhp_next_state(bringup, &state, st, target)) {
> +		int err;
> +
>  		err = cpuhp_invoke_callback(cpu, state, bringup, NULL, NULL);
> -		if (err)
> +		if (!err)
> +			continue;
> +
> +		if (nofail) {
> +			pr_warn("CPU %u %s state %s (%d) failed (%d)\n",
> +				cpu, bringup ? "UP" : "DOWN",
> +				cpuhp_get_step(st->state)->name,
> +				st->state, err);
> +			ret = -1;
> +		} else {
> +			ret = err;
>  			break;
> +		}
>  	}
>  
> -	return err;
> +	return ret;
> +}
> +
> +static inline int cpuhp_invoke_callback_range(bool bringup,
> +					      unsigned int cpu,
> +					      struct cpuhp_cpu_state *st,
> +					      enum cpuhp_state target)
> +{
> +	return _cpuhp_invoke_callback_range(bringup, cpu, st, target, false);
> +}
> +
> +static inline void cpuhp_invoke_callback_range_nofail(bool bringup,
> +						      unsigned int cpu,
> +						      struct cpuhp_cpu_state *st,
> +						      enum cpuhp_state target)
> +{
> +	WARN_ON_ONCE(_cpuhp_invoke_callback_range(bringup, cpu, st, target, true));
>  }
>  
>  static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
> @@ -999,7 +1029,6 @@ static int take_cpu_down(void *_param)
>  	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
>  	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
>  	int err, cpu = smp_processor_id();
> -	int ret;
>  
>  	/* Ensure this CPU doesn't handle any more interrupts. */
>  	err = __cpu_disable();
> @@ -1012,13 +1041,11 @@ static int take_cpu_down(void *_param)
>  	 */
>  	WARN_ON(st->state != (CPUHP_TEARDOWN_CPU - 1));
>  
> -	/* Invoke the former CPU_DYING callbacks */
> -	ret = cpuhp_invoke_callback_range(false, cpu, st, target);
> -
>  	/*
> +	 * Invoke the former CPU_DYING callbacks
>  	 * DYING must not fail!
>  	 */
> -	WARN_ON_ONCE(ret);
> +	cpuhp_invoke_callback_range_nofail(false, cpu, st, target);
>  
>  	/* Give up timekeeping duties */
>  	tick_handover_do_timer();
> @@ -1296,16 +1323,14 @@ void notify_cpu_starting(unsigned int cpu)
>  {
>  	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
>  	enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
> -	int ret;
>  
>  	rcu_cpu_starting(cpu);	/* Enables RCU usage on this CPU. */
>  	cpumask_set_cpu(cpu, &cpus_booted_once_mask);
> -	ret = cpuhp_invoke_callback_range(true, cpu, st, target);
>  
>  	/*
>  	 * STARTING must not fail!
>  	 */
> -	WARN_ON_ONCE(ret);
> +	cpuhp_invoke_callback_range_nofail(true, cpu, st, target);
>  }
>  
>  /*
>