Date:   Thu, 10 Nov 2022 17:45:50 +0100
From:   Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>
To:     fenghua.yu@...el.com, jdelvare@...e.com, linux@...ck-us.net,
        Robin Murphy <robin.murphy@....com>
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux.dev, lucas.demarchi@...el.com
Subject: Re: [PATCH] hwmon/coretemp: Simplify platform device antics

Hi Robin,

On Thursday, 10 November 2022 17:20:25 CET Robin Murphy wrote:
> Coretemp's vestigial platform driver is odd. All the real work is done
> globally by the initcall and CPU hotplug notifiers, while the "driver"
> effectively just wraps an allocation and the registration of the hwmon
> interface in a long-winded round-trip through the driver core. The whole
> logic of dynamically creating and destroying platform devices to bring
> the interfaces up and down is fatally flawed right away, since it
> assumes platform_device_add() will synchronously bind the driver and set
> drvdata before it returns, thus results in a NULL dereference if
> drivers_autoprobe is turned off for the platform bus. Furthermore, the
> unusual approach of doing that from within a CPU hotplug notifier is
> also problematic. It's already commented in the code that it deadlocks
> suspend, but it also causes lockdep issues for other drivers or
> subsystems which may want to legitimately register a CPU hotplug
> notifier from a platform bus notifier.
> 
> All of these issues can be solved by ripping this questionable behaviour
> out completely, simply tying the platform devices to the lifetime of the
> module itself, and directly managing the hwmon interfaces from the
> hotplug notifiers. There is a slight user-visible change in that
> /sys/bus/platform/drivers/coretemp will no longer appear, and
> /sys/devices/platform/coretemp.n will remain present if package n is
> hotplugged off, but hwmon users should really only be looking for the
> presence of the hwmon interfaces, whose behaviour remains unchanged.
> 
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> 
> I haven't been able to fully test hotplug since I only have a
> single-socket Intel system to hand.

I'll give it a try on our intel-gfx-trybot, together with our former iommu 
workaround reverted.

Thanks,
Janusz

> 
>  drivers/hwmon/coretemp.c | 134 ++++++++++++++++++---------------------
>  1 file changed, 61 insertions(+), 73 deletions(-)
> 
> diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
> index 8bf32c6c85d9..9fa68a81625e 100644
> --- a/drivers/hwmon/coretemp.c
> +++ b/drivers/hwmon/coretemp.c
> @@ -543,66 +543,49 @@ static void coretemp_remove_core(struct platform_data 
*pdata, int indx)
>  		ida_free(&pdata->ida, indx - BASE_SYSFS_ATTR_NO);
>  }
>  
> -static int coretemp_probe(struct platform_device *pdev)
> +static int coretemp_device_add(int zoneid)
>  {
> -	struct device *dev = &pdev->dev;
> +	struct platform_device *pdev;
>  	struct platform_data *pdata;
> +	int err;
>  
>  	/* Initialize the per-zone data structures */
> -	pdata = devm_kzalloc(dev, sizeof(struct platform_data), 
GFP_KERNEL);
> +	pdata = kzalloc(sizeof(*pdata), GFP_KERNEL);
>  	if (!pdata)
>  		return -ENOMEM;
>  
> -	pdata->pkg_id = pdev->id;
> +	pdata->pkg_id = zoneid;
>  	ida_init(&pdata->ida);
> -	platform_set_drvdata(pdev, pdata);
> -
> -	pdata->hwmon_dev = devm_hwmon_device_register_with_groups(dev, 
DRVNAME,
> -								
  pdata, NULL);
> -	return PTR_ERR_OR_ZERO(pdata->hwmon_dev);
> -}
> -
> -static int coretemp_remove(struct platform_device *pdev)
> -{
> -	struct platform_data *pdata = platform_get_drvdata(pdev);
> -	int i;
> -
> -	for (i = MAX_CORE_DATA - 1; i >= 0; --i)
> -		if (pdata->core_data[i])
> -			coretemp_remove_core(pdata, i);
> -
> -	ida_destroy(&pdata->ida);
> -	return 0;
> -}
> -
> -static struct platform_driver coretemp_driver = {
> -	.driver = {
> -		.name = DRVNAME,
> -	},
> -	.probe = coretemp_probe,
> -	.remove = coretemp_remove,
> -};
> -
> -static struct platform_device *coretemp_device_add(unsigned int cpu)
> -{
> -	int err, zoneid = topology_logical_die_id(cpu);
> -	struct platform_device *pdev;
> -
> -	if (zoneid < 0)
> -		return ERR_PTR(-ENOMEM);
>  
>  	pdev = platform_device_alloc(DRVNAME, zoneid);
> -	if (!pdev)
> -		return ERR_PTR(-ENOMEM);
> -
> -	err = platform_device_add(pdev);
> -	if (err) {
> -		platform_device_put(pdev);
> -		return ERR_PTR(err);
> +	if (!pdev) {
> +		err = -ENOMEM;
> +		goto err_free_pdata;
>  	}
>  
> +	err = platform_device_add(pdev);
> +	if (err)
> +		goto err_put_dev;
> +
> +	platform_set_drvdata(pdev, pdata);
>  	zone_devices[zoneid] = pdev;
> -	return pdev;
> +	return 0;
> +
> +err_put_dev:
> +	platform_device_put(pdev);
> +err_free_pdata:
> +	kfree(pdata);
> +	return err;
> +}
> +
> +static void coretemp_device_remove(int zoneid)
> +{
> +	struct platform_device *pdev = zone_devices[zoneid];
> +	struct platform_data *pdata = platform_get_drvdata(pdev);
> +
> +	ida_destroy(&pdata->ida);
> +	kfree(pdata);
> +	platform_device_unregister(pdev);
>  }
>  
>  static int coretemp_cpu_online(unsigned int cpu)
> @@ -626,7 +609,10 @@ static int coretemp_cpu_online(unsigned int cpu)
>  	if (!cpu_has(c, X86_FEATURE_DTHERM))
>  		return -ENODEV;
>  
> -	if (!pdev) {
> +	pdata = platform_get_drvdata(pdev);
> +	if (!pdata->hwmon_dev) {
> +		struct device *hwmon;
> +
>  		/* Check the microcode version of the CPU */
>  		if (chk_ucode_version(cpu))
>  			return -EINVAL;
> @@ -637,9 +623,11 @@ static int coretemp_cpu_online(unsigned int cpu)
>  		 * online. So, initialize per-pkg data structures and
>  		 * then bring this core online.
>  		 */
> -		pdev = coretemp_device_add(cpu);
> -		if (IS_ERR(pdev))
> -			return PTR_ERR(pdev);
> +		hwmon = hwmon_device_register_with_groups(&pdev->dev, 
DRVNAME,
> +							  
pdata, NULL);
> +		if (IS_ERR(hwmon))
> +			return PTR_ERR(hwmon);
> +		pdata->hwmon_dev = hwmon;
>  
>  		/*
>  		 * Check whether pkgtemp support is available.
> @@ -649,7 +637,6 @@ static int coretemp_cpu_online(unsigned int cpu)
>  			coretemp_add_core(pdev, cpu, 1);
>  	}
>  
> -	pdata = platform_get_drvdata(pdev);
>  	/*
>  	 * Check whether a thread sibling is already online. If not add the
>  	 * interface for this CPU core.
> @@ -668,18 +655,14 @@ static int coretemp_cpu_offline(unsigned int cpu)
>  	struct temp_data *tdata;
>  	int i, indx = -1, target;
>  
> -	/*
> -	 * Don't execute this on suspend as the device remove locks
> -	 * up the machine.
> -	 */
> +	/* No need to tear down any interfaces for suspend */
>  	if (cpuhp_tasks_frozen)
>  		return 0;
>  
>  	/* If the physical CPU device does not exist, just return */
> -	if (!pdev)
> -		return 0;
> -
>  	pd = platform_get_drvdata(pdev);
> +	if (!pd->hwmon_dev)
> +		return 0;
>  
>  	for (i = 0; i < NUM_REAL_CORES; i++) {
>  		if (pd->cpu_map[i] == topology_core_id(cpu)) {
> @@ -711,13 +694,14 @@ static int coretemp_cpu_offline(unsigned int cpu)
>  	}
>  
>  	/*
> -	 * If all cores in this pkg are offline, remove the device. This
> -	 * will invoke the platform driver remove function, which cleans up
> -	 * the rest.
> +	 * If all cores in this pkg are offline, remove the interface.
>  	 */
> +	tdata = pd->core_data[PKG_SYSFS_ATTR_NO];
>  	if (cpumask_empty(&pd->cpumask)) {
> -		zone_devices[topology_logical_die_id(cpu)] = NULL;
> -		platform_device_unregister(pdev);
> +		if (tdata)
> +			coretemp_remove_core(pd, PKG_SYSFS_ATTR_NO);
> +		hwmon_device_unregister(pd->hwmon_dev);
> +		pd->hwmon_dev = NULL;
>  		return 0;
>  	}
>  
> @@ -725,7 +709,6 @@ static int coretemp_cpu_offline(unsigned int cpu)
>  	 * Check whether this core is the target for the package
>  	 * interface. We need to assign it to some other cpu.
>  	 */
> -	tdata = pd->core_data[PKG_SYSFS_ATTR_NO];
>  	if (tdata && tdata->cpu == cpu) {
>  		target = cpumask_first(&pd->cpumask);
>  		mutex_lock(&tdata->update_lock);
> @@ -744,7 +727,7 @@ static enum cpuhp_state coretemp_hp_online;
>  
>  static int __init coretemp_init(void)
>  {
> -	int err;
> +	int i, err;
>  
>  	/*
>  	 * CPUID.06H.EAX[0] indicates whether the CPU has thermal
> @@ -760,20 +743,22 @@ static int __init coretemp_init(void)
>  	if (!zone_devices)
>  		return -ENOMEM;
>  
> -	err = platform_driver_register(&coretemp_driver);
> -	if (err)
> -		goto outzone;
> +	for (i = 0; i < max_zones; i++) {
> +		err = coretemp_device_add(i);
> +		if (err)
> +			goto outzone;
> +	}
>  
>  	err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "hwmon/
coretemp:online",
>  				coretemp_cpu_online, 
coretemp_cpu_offline);
>  	if (err < 0)
> -		goto outdrv;
> +		goto outzone;
>  	coretemp_hp_online = err;
>  	return 0;
>  
> -outdrv:
> -	platform_driver_unregister(&coretemp_driver);
>  outzone:
> +	while (i--)
> +		coretemp_device_remove(i);
>  	kfree(zone_devices);
>  	return err;
>  }
> @@ -781,8 +766,11 @@ module_init(coretemp_init)
>  
>  static void __exit coretemp_exit(void)
>  {
> +	int i;
> +
>  	cpuhp_remove_state(coretemp_hp_online);
> -	platform_driver_unregister(&coretemp_driver);
> +	for (i = 0; i < max_zones; i++)
> +		coretemp_device_remove(i);
>  	kfree(zone_devices);
>  }
>  module_exit(coretemp_exit)
> 

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