Date:   Mon, 14 Nov 2022 09:46:35 +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

On Thursday, 10 November 2022 17:45:50 CET Janusz Krzysztofik wrote:
> 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.

With our local iommu workaround reverted, 5 out of 37 test machines failed to 
boot cleanly, and 1 other machine failed to wake up cleanly from S3, all due 
to coretemp / iommu lockdep splat reported.
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110806v1/bat-all.html?testfilter=@load%7Cs3-without-i915%7Cabort
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110806v1/bat-adlp-6/boot0.txt
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110806v1/fi-kbl-soraka/boot0.txt
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110806v1/fi-kbl-x1275/boot0.txt
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110806v1/fi-apl-guc/boot0.txt
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110806v1/fi-skl-guc/boot0.txt
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110806v1/bat-rpls-1/dmesg0.txt

With this coretemp patch on top, the lockdep splat was not reported on any 
machine.
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_110768v1/bat-all.html?testfilter=@load%7Cs3-without-i915%7Cabort

This patch seems to fix the coretemp / iommu lockdep splat issue.

Tested-by: Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>


> 
> 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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