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Date: Tue, 30 Apr 2024 11:13:41 +0100
From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
To: Gavin Shan <gshan@redhat.com>
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Subject: Re: [PATCH v8 04/16] ACPI: processor: Move checks and availability
 of acpi_processor earlier
Message-ID: <20240430111341.00003dba@huawei.com>
In-Reply-To: <20240430102838.00006e04@Huawei.com>
References: <20240426135126.12802-1-Jonathan.Cameron@huawei.com>
	<20240426135126.12802-5-Jonathan.Cameron@huawei.com>
	<80a2e07f-ecb2-48af-b2be-646f17e0e63e@redhat.com>
	<20240430102838.00006e04@Huawei.com>
Organization: Huawei Technologies R&D (UK) Ltd.
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On Tue, 30 Apr 2024 10:28:38 +0100
Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:

> On Tue, 30 Apr 2024 14:17:24 +1000
> Gavin Shan <gshan@redhat.com> wrote:
> 
> > On 4/26/24 23:51, Jonathan Cameron wrote:  
> > > Make the per_cpu(processors, cpu) entries available earlier so that
> > > they are available in arch_register_cpu() as ARM64 will need access
> > > to the acpi_handle to distinguish between acpi_processor_add()
> > > and earlier registration attempts (which will fail as _STA cannot
> > > be checked).
> > > 
> > > Reorder the remove flow to clear this per_cpu() after
> > > arch_unregister_cpu() has completed, allowing it to be used in
> > > there as well.
> > > 
> > > Note that on x86 for the CPU hotplug case, the pr->id prior to
> > > acpi_map_cpu() may be invalid. Thus the per_cpu() structures
> > > must be initialized after that call or after checking the ID
> > > is valid (not hotplug path).
> > > 
> > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > 
> > > ---
> > > v8: On buggy bios detection when setting per_cpu structures
> > >      do not carry on.
> > >      Fix up the clearing of per cpu structures to remove unwanted
> > >      side effects and ensure an error code isn't use to reference them.
> > > ---
> > >   drivers/acpi/acpi_processor.c | 79 +++++++++++++++++++++--------------
> > >   1 file changed, 48 insertions(+), 31 deletions(-)
> > > 
> > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > index ba0a6f0ac841..3b180e21f325 100644
> > > --- a/drivers/acpi/acpi_processor.c
> > > +++ b/drivers/acpi/acpi_processor.c
> > > @@ -183,8 +183,38 @@ static void __init acpi_pcc_cpufreq_init(void) {}
> > >   #endif /* CONFIG_X86 */
> > >   
> > >   /* Initialization */
> > > +static DEFINE_PER_CPU(void *, processor_device_array);
> > > +
> > > +static bool acpi_processor_set_per_cpu(struct acpi_processor *pr,
> > > +				       struct acpi_device *device)
> > > +{
> > > +	BUG_ON(pr->id >= nr_cpu_ids);    
> > 
> > One blank line after BUG_ON() if we need to follow original implementation.  
> 
> Sure unintentional - I'll put that back.
> 
> >   
> > > +	/*
> > > +	 * Buggy BIOS check.
> > > +	 * ACPI id of processors can be reported wrongly by the BIOS.
> > > +	 * Don't trust it blindly
> > > +	 */
> > > +	if (per_cpu(processor_device_array, pr->id) != NULL &&
> > > +	    per_cpu(processor_device_array, pr->id) != device) {
> > > +		dev_warn(&device->dev,
> > > +			 "BIOS reported wrong ACPI id %d for the processor\n",
> > > +			 pr->id);
> > > +		/* Give up, but do not abort the namespace scan. */    
> > 
> > It depends on how the return value is handled by the caller if the namespace
> > is continued to be scanned. The caller can be acpi_processor_hotadd_init()
> > and acpi_processor_get_info() after this patch is applied. So I think this
> > specific comment need to be moved to the caller.  
> 
> Good point. This gets messy and was an unintended change.
> 
> Previously the options were:
> 1) acpi_processor_get_info() failed for other reasons - this code was never called.
> 2) acpi_processor_get_info() succeeded without acpi_processor_hotadd_init (non hotplug)
>    this code then ran and would paper over the problem doing a bunch of cleanup under err.
> 3) acpi_processor_get_info() succeeded with acpi_processor_hotadd_init called.
>    This code then ran and would paper over the problem doing a bunch of cleanup under err.
> 
> We should maintain that or argue cleanly against it.
> 
> This isn't helped the the fact I have no idea which cases we care about for that bios
> bug handling.  Do any of those bios's ever do hotplug?  Guess we have to try and maintain
> whatever protection this was offering.
> 
> Also, the original code leaks data in some paths and I have limited idea
> of whether it is intentional or not. So to tidy the issue up that you've identified
> I'll need to try and make that code consistent first.
> 
> I suspect the only way to do that is going to be to duplicate the allocations we
> 'want' to leak to deal with the bios bug detection.
> 
> For example acpi_processor_get_info() failing leaks pr and pr->throttling.shared_cpu_map
> before this series. After this series we need pr to leak because it's used for the detection
> via processor_device_array.
> 
> I'll work through this but it's going to be tricky to tell if we get right.
> Step 1 will be closing the existing leaks and then we will have something
> consistent to build on.
> 
I 'think' that fixing the original leaks makes this all much more straight forward.
That return 0 for acpi_processor_get_info() never made sense as far as I can tell.
The pr isn't used after this point.

What about something along lines of.

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 161c95c9d60a..97cff4492304 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -392,8 +392,10 @@ static int acpi_processor_add(struct acpi_device *device,
        device->driver_data = pr;

        result = acpi_processor_get_info(device);
-       if (result) /* Processor is not physically present or unavailable */
-               return 0;
+       if (result) { /* Processor is not physically present or unavailable */
+               result = 0;
+               goto err_free_throttling_mask;
+       }

        BUG_ON(pr->id >= nr_cpu_ids);

@@ -408,7 +410,7 @@ static int acpi_processor_add(struct acpi_device *device,
                        "BIOS reported wrong ACPI id %d for the processor\n",
                        pr->id);
                /* Give up, but do not abort the namespace scan. */
-               goto err;
+               goto err_clear_driver_data;
        }
        /*
         * processor_device_array is not cleared on errors to allow buggy BIOS
@@ -420,12 +422,12 @@ static int acpi_processor_add(struct acpi_device *device,
        dev = get_cpu_device(pr->id);
        if (!dev) {
                result = -ENODEV;
-               goto err;
+               goto err_clear_per_cpu;
        }

        result = acpi_bind_one(dev, device);
        if (result)
-               goto err;
+               goto err_clear_per_cpu;

        pr->dev = dev;

@@ -436,10 +438,12 @@ static int acpi_processor_add(struct acpi_device *device,
        dev_err(dev, "Processor driver could not be attached\n");
        acpi_unbind_one(dev);

- err:
-       free_cpumask_var(pr->throttling.shared_cpu_map);
-       device->driver_data = NULL;
+ err_clear_per_cpu:
        per_cpu(processors, pr->id) = NULL;
+ err_clear_driver_data:
+       device->driver_data = NULL;
+ err_free_throttling_mask:
+       free_cpumask_var(pr->throttling.shared_cpu_map);
  err_free_pr:
        kfree(pr);
        return result;

Then the diff on this patch is simply:

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 3c49eae1e943..3b75f5aeb7ab 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -200,7 +200,6 @@ static bool acpi_processor_set_per_cpu(struct acpi_processor *pr,
                dev_warn(&device->dev,
                         "BIOS reported wrong ACPI id %d for the processor\n",
                         pr->id);
-               /* Give up, but do not abort the namespace scan. */
                return false;
        }
        /*
@@ -230,13 +229,14 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr,
                goto out;

        if (!acpi_processor_set_per_cpu(pr, device)) {
+               ret = -EINVAL;
                acpi_unmap_cpu(pr->id);
                goto out;
        }

        ret = arch_register_cpu(pr->id);
        if (ret) {
-               /* Leave the processor device array in place to detect buggy bios */
+x              /* Leave the processor device array in place to detect buggy bios */
                per_cpu(processors, pr->id) = NULL;
                acpi_unmap_cpu(pr->id);
                goto out;
@@ -262,7 +262,7 @@ static inline int acpi_processor_hotadd_init(struct acpi_processor *pr,
 }
 #endif /* CONFIG_ACPI_HOTPLUG_CPU */

-static int acpi_processor_get_info(struct acpi_device *device)
+static int acpi_processor_get_info(struct acpi_device *device, bool bios_bug)
 {
        union acpi_object object = { 0 };
        struct acpi_buffer buffer = { sizeof(union acpi_object), &object };
@@ -361,7 +361,7 @@ static int acpi_processor_get_info(struct acpi_device *device)
                        return ret;
        } else {
                if (!acpi_processor_set_per_cpu(pr, device))
-                       return 0;
+                       return -EINVAL;
        }

        /*
> > 
> > Besides, it seems acpi_processor_set_per_cpu() isn't properly called and
> > memory leakage can happen. More details are given below.
> >   
> > > +		return false;
> > > +	}
> > > +	/*
> > > +	 * processor_device_array is not cleared on errors to allow buggy BIOS
> > > +	 * checks.
> > > +	 */
> > > +	per_cpu(processor_device_array, pr->id) = device;
> > > +	per_cpu(processors, pr->id) = pr;
> > > +
> > > +	return true;
> > > +}
> > > +
> > >   #ifdef CONFIG_ACPI_HOTPLUG_CPU
> > > -static int acpi_processor_hotadd_init(struct acpi_processor *pr)
> > > +static int acpi_processor_hotadd_init(struct acpi_processor *pr,
> > > +				      struct acpi_device *device)
> > >   {
> > >   	int ret;
> > >   
> > > @@ -198,8 +228,15 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
> > >   	if (ret)
> > >   		goto out;
> > >   
> > > +	if (!acpi_processor_set_per_cpu(pr, device)) {
> > > +		acpi_unmap_cpu(pr->id);
> > > +		goto out;
> > > +	}
> > > +    
> > 
> > With the 'goto out', zero is returned from acpi_processor_hotadd_init() to acpi_processor_get_info().

Indeed a bug :(

> > The zero return value is carried from acpi_map_cpu() in acpi_processor_hotadd_init(). If I'm correct,
> > we need return errno from acpi_processor_get_info() to acpi_processor_add() so that cleanup can be
> > done. For example, the cleanup corresponding to the 'err' tag can be done in acpi_processor_add().
> > Otherwise, we will have memory leakage.

The confusion here was that previously acpi_processor_add() was missing error cleanup for
acpi_processor_get_info().  With that in place I think it's all much simpler.

Thanks for your eagle eyes!

Jonathan


> >   
> > >   	ret = arch_register_cpu(pr->id);
> > >   	if (ret) {
> > > +		/* Leave the processor device array in place to detect buggy bios */
> > > +		per_cpu(processors, pr->id) = NULL;
> > >   		acpi_unmap_cpu(pr->id);
> > >   		goto out;
> > >   	}
> > > @@ -217,7 +254,8 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
> > >   	return ret;
> > >   }
> > >   #else
> > > -static inline int acpi_processor_hotadd_init(struct acpi_processor *pr)
> > > +static inline int acpi_processor_hotadd_init(struct acpi_processor *pr,
> > > +					     struct acpi_device *device)
> > >   {
> > >   	return -ENODEV;
> > >   }
> > > @@ -316,10 +354,13 @@ static int acpi_processor_get_info(struct acpi_device *device)
> > >   	 *  because cpuid <-> apicid mapping is persistent now.
> > >   	 */
> > >   	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> > > -		int ret = acpi_processor_hotadd_init(pr);
> > > +		int ret = acpi_processor_hotadd_init(pr, device);
> > >   
> > >   		if (ret)
> > >   			return ret;
> > > +	} else {
> > > +		if (!acpi_processor_set_per_cpu(pr, device))
> > > +			return 0;
> > >   	}
> > >       
> > 
> > For non-hotplug case, we still need pass the error to acpi_processor_add() so that
> > cleanup corresponding 'err' tag can be done. Otherwise, we will have memory leakage.
> >   
> > >   	/*
> > > @@ -365,8 +406,6 @@ static int acpi_processor_get_info(struct acpi_device *device)
> > >    * (cpu_data(cpu)) values, like CPU feature flags, family, model, etc.
> > >    * Such things have to be put in and set up by the processor driver's .probe().
> > >    */
> > > -static DEFINE_PER_CPU(void *, processor_device_array);
> > > -
> > >   static int acpi_processor_add(struct acpi_device *device,
> > >   					const struct acpi_device_id *id)
> > >   {
> > > @@ -395,28 +434,6 @@ static int acpi_processor_add(struct acpi_device *device,
> > >   	if (result) /* Processor is not physically present or unavailable */
> > >   		return 0;
> > >   
> > > -	BUG_ON(pr->id >= nr_cpu_ids);
> > > -
> > > -	/*
> > > -	 * Buggy BIOS check.
> > > -	 * ACPI id of processors can be reported wrongly by the BIOS.
> > > -	 * Don't trust it blindly
> > > -	 */
> > > -	if (per_cpu(processor_device_array, pr->id) != NULL &&
> > > -	    per_cpu(processor_device_array, pr->id) != device) {
> > > -		dev_warn(&device->dev,
> > > -			"BIOS reported wrong ACPI id %d for the processor\n",
> > > -			pr->id);
> > > -		/* Give up, but do not abort the namespace scan. */
> > > -		goto err;
> > > -	}
> > > -	/*
> > > -	 * processor_device_array is not cleared on errors to allow buggy BIOS
> > > -	 * checks.
> > > -	 */
> > > -	per_cpu(processor_device_array, pr->id) = device;
> > > -	per_cpu(processors, pr->id) = pr;
> > > -
> > >   	dev = get_cpu_device(pr->id);
> > >   	if (!dev) {
> > >   		result = -ENODEV;
> > > @@ -469,10 +486,6 @@ static void acpi_processor_remove(struct acpi_device *device)
> > >   	device_release_driver(pr->dev);
> > >   	acpi_unbind_one(pr->dev);
> > >   
> > > -	/* Clean up. */
> > > -	per_cpu(processor_device_array, pr->id) = NULL;
> > > -	per_cpu(processors, pr->id) = NULL;
> > > -
> > >   	cpu_maps_update_begin();
> > >   	cpus_write_lock();
> > >   
> > > @@ -480,6 +493,10 @@ static void acpi_processor_remove(struct acpi_device *device)
> > >   	arch_unregister_cpu(pr->id);
> > >   	acpi_unmap_cpu(pr->id);
> > >   
> > > +	/* Clean up. */
> > > +	per_cpu(processor_device_array, pr->id) = NULL;
> > > +	per_cpu(processors, pr->id) = NULL;
> > > +
> > >   	cpus_write_unlock();
> > >   	cpu_maps_update_done();
> > >       
> > 
> > Thanks,
> > Gavin
> >   
>