linux-kernel - Re: [patch V3 12/32] hwtracing/coresight-etm4x: Use cpuhp_setup_state_nocalls

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Date:   Thu, 25 May 2017 10:47:00 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [patch V3 12/32] hwtracing/coresight-etm4x: Use
 cpuhp_setup_state_nocalls_cpuslocked()

On Wed, May 24, 2017 at 10:15:23AM +0200, Thomas Gleixner wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> etm_probe4() holds get_online_cpus() while invoking
> cpuhp_setup_state_nocalls().
> 
> cpuhp_setup_state_nocalls() invokes get_online_cpus() as well. This is
> correct, but prevents the conversion of the hotplug locking to a percpu
> rwsem.
> 
> Use cpuhp_setup_state_nocalls_cpuslocked() to avoid the nested
> call. Convert *_online_cpus() to the new interfaces while at it.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: linux-arm-kernel@...ts.infradead.org

Acked-by: Mathieu Poirier <mathieu.poirier@...aro.org>

> 
> ---
>  drivers/hwtracing/coresight/coresight-etm4x.c |   20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> @@ -371,7 +371,7 @@ static void etm4_disable_sysfs(struct co
>  	 * after cpu online mask indicates the cpu is offline but before the
>  	 * DYING hotplug callback is serviced by the ETM driver.
>  	 */
> -	get_online_cpus();
> +	cpus_read_lock();
>  	spin_lock(&drvdata->spinlock);
>  
>  	/*
> @@ -381,7 +381,7 @@ static void etm4_disable_sysfs(struct co
>  	smp_call_function_single(drvdata->cpu, etm4_disable_hw, drvdata, 1);
>  
>  	spin_unlock(&drvdata->spinlock);
> -	put_online_cpus();
> +	cpus_read_unlock();
>  
>  	dev_info(drvdata->dev, "ETM tracing disabled\n");
>  }
> @@ -982,7 +982,7 @@ static int etm4_probe(struct amba_device
>  
>  	drvdata->cpu = pdata ? pdata->cpu : 0;
>  
> -	get_online_cpus();
> +	cpus_read_lock();
>  	etmdrvdata[drvdata->cpu] = drvdata;
>  
>  	if (smp_call_function_single(drvdata->cpu,
> @@ -990,18 +990,18 @@ static int etm4_probe(struct amba_device
>  		dev_err(dev, "ETM arch init failed\n");
>  
>  	if (!etm4_count++) {
> -		cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING,
> -					  "arm/coresight4:starting",
> -					  etm4_starting_cpu, etm4_dying_cpu);
> -		ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> -						"arm/coresight4:online",
> -						etm4_online_cpu, NULL);
> +		cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING,
> +						     "arm/coresight4:starting",
> +						     etm4_starting_cpu, etm4_dying_cpu);
> +		ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ONLINE_DYN,
> +							   "arm/coresight4:online",
> +							   etm4_online_cpu, NULL);
>  		if (ret < 0)
>  			goto err_arch_supported;
>  		hp_online = ret;
>  	}
>  
> -	put_online_cpus();
> +	cpus_read_unlock();
>  
>  	if (etm4_arch_supported(drvdata->arch) == false) {
>  		ret = -EINVAL;
> 
>