[PATCH] drm/i915: tidy up gen8_init_scratch

[PATCH] drm/i915: tidy up gen8_init_scratch

[Matthew Auld]

Use goto teardown path and also ensure we reset any struct members which
would otherwise contain an error encoded pointer, and could be mistaken
for a valid address.

Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 36 +++++++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 0d666b3..a723b74 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -866,31 +866,31 @@ static void gen8_free_page_tables(struct drm_device *dev,
 static int gen8_init_scratch(struct i915_address_space *vm)
 {
 	struct drm_device *dev = vm->dev;
+	int ret;
 
 	vm->scratch_page = alloc_scratch_page(dev);
-	if (IS_ERR(vm->scratch_page))
-		return PTR_ERR(vm->scratch_page);
+	if (IS_ERR(vm->scratch_page)) {
+		ret = PTR_ERR(vm->scratch_page);
+		goto fail_scratch;
+	}
 
 	vm->scratch_pt = alloc_pt(dev);
 	if (IS_ERR(vm->scratch_pt)) {
-		free_scratch_page(dev, vm->scratch_page);
-		return PTR_ERR(vm->scratch_pt);
+		ret = PTR_ERR(vm->scratch_pt);
+		goto fail_pt;
 	}
 
 	vm->scratch_pd = alloc_pd(dev);
 	if (IS_ERR(vm->scratch_pd)) {
-		free_pt(dev, vm->scratch_pt);
-		free_scratch_page(dev, vm->scratch_page);
-		return PTR_ERR(vm->scratch_pd);
+		ret = PTR_ERR(vm->scratch_pd);
+		goto fail_pd;
 	}
 
 	if (USES_FULL_48BIT_PPGTT(dev)) {
 		vm->scratch_pdp = alloc_pdp(dev);
 		if (IS_ERR(vm->scratch_pdp)) {
-			free_pd(dev, vm->scratch_pd);
-			free_pt(dev, vm->scratch_pt);
-			free_scratch_page(dev, vm->scratch_page);
-			return PTR_ERR(vm->scratch_pdp);
+			ret = PTR_ERR(vm->scratch_pdp);
+			goto fail_pdp;
 		}
 	}
 
@@ -900,6 +900,20 @@ static int gen8_init_scratch(struct i915_address_space *vm)
 		gen8_initialize_pdp(vm, vm->scratch_pdp);
 
 	return 0;
+
+fail_pdp:
+	vm->scratch_pdp = NULL;
+	free_pd(dev, vm->scratch_pd);
+fail_pd:
+	vm->scratch_pd = NULL;
+	free_pt(dev, vm->scratch_pt);
+fail_pt:
+	vm->scratch_pt = NULL;
+	free_scratch_page(dev, vm->scratch_page);
+fail_scratch:
+	vm->scratch_page = NULL;
+
+	return ret;
 }
 
 static int gen8_ppgtt_notify_vgt(struct i915_hw_ppgtt *ppgtt, bool create)
-- 
2.4.11

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✗ Fi.CI.BAT: failure for drm/i915: tidy up gen8_init_scratch

[Patchwork]

== Series Details ==

Series: drm/i915: tidy up gen8_init_scratch
URL   : https://patchwork.freedesktop.org/series/6315/
State : failure

== Summary ==

Series 6315v1 drm/i915: tidy up gen8_init_scratch
http://patchwork.freedesktop.org/api/1.0/series/6315/revisions/1/mbox/

Test kms_pipe_crc_basic:
        Subgroup hang-read-crc-pipe-b:
                pass       -> INCOMPLETE (snb-dellxps)

bdw-nuci7        total:200  pass:188  dwarn:0   dfail:0   fail:0   skip:12 
bdw-ultra        total:200  pass:175  dwarn:0   dfail:0   fail:0   skip:25 
bsw-nuc-2        total:199  pass:158  dwarn:0   dfail:0   fail:0   skip:41 
byt-nuc          total:199  pass:158  dwarn:0   dfail:0   fail:0   skip:41 
hsw-brixbox      total:200  pass:174  dwarn:0   dfail:0   fail:0   skip:26 
hsw-gt2          total:200  pass:178  dwarn:0   dfail:0   fail:1   skip:21 
ilk-hp8440p      total:200  pass:139  dwarn:0   dfail:0   fail:0   skip:61 
ivb-t430s        total:200  pass:169  dwarn:0   dfail:0   fail:0   skip:31 
skl-i7k-2        total:200  pass:173  dwarn:0   dfail:0   fail:0   skip:27 
skl-nuci5        total:200  pass:189  dwarn:0   dfail:0   fail:0   skip:11 
snb-dellxps      total:158  pass:118  dwarn:0   dfail:0   fail:0   skip:39 
snb-x220t        total:200  pass:158  dwarn:0   dfail:0   fail:1   skip:41 

Results at /archive/results/CI_IGT_test/Patchwork_2070/

9478b817812b1bf74a5e59f7d5f8220e0df20415 drm-intel-nightly: 2016y-04m-26d-11h-29m-24s UTC integration manifest
b990c46 drm/i915: tidy up gen8_init_scratch

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Re: [PATCH] drm/i915: tidy up gen8_init_scratch

[Joonas Lahtinen]

On ti, 2016-04-26 at 10:27 +0100, Matthew Auld wrote:
> Use goto teardown path and also ensure we reset any struct members which
> would otherwise contain an error encoded pointer, and could be mistaken
> for a valid address.
> 
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>

As this goes through the whole function, good idea to check with git
blame for the function author and CC (in this case Mika, added as CC).

> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 36 +++++++++++++++++++++++++-----------
>  1 file changed, 25 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 0d666b3..a723b74 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -866,31 +866,31 @@ static void gen8_free_page_tables(struct drm_device *dev,
>  static int gen8_init_scratch(struct i915_address_space *vm)
>  {
>  	struct drm_device *dev = vm->dev;
> +	int ret;
>  
>  	vm->scratch_page = alloc_scratch_page(dev);
> -	if (IS_ERR(vm->scratch_page))
> -		return PTR_ERR(vm->scratch_page);
> +	if (IS_ERR(vm->scratch_page)) {
> +		ret = PTR_ERR(vm->scratch_page);
> +		goto fail_scratch;
> +	}
>  
>  	vm->scratch_pt = alloc_pt(dev);
>  	if (IS_ERR(vm->scratch_pt)) {
> -		free_scratch_page(dev, vm->scratch_page);
> -		return PTR_ERR(vm->scratch_pt);
> +		ret = PTR_ERR(vm->scratch_pt);
> +		goto fail_pt;
>  	}
>  
>  	vm->scratch_pd = alloc_pd(dev);
>  	if (IS_ERR(vm->scratch_pd)) {
> -		free_pt(dev, vm->scratch_pt);
> -		free_scratch_page(dev, vm->scratch_page);
> -		return PTR_ERR(vm->scratch_pd);
> +		ret = PTR_ERR(vm->scratch_pd);
> +		goto fail_pd;
>  	}
>  
>  	if (USES_FULL_48BIT_PPGTT(dev)) {
>  		vm->scratch_pdp = alloc_pdp(dev);
>  		if (IS_ERR(vm->scratch_pdp)) {
> -			free_pd(dev, vm->scratch_pd);
> -			free_pt(dev, vm->scratch_pt);
> -			free_scratch_page(dev, vm->scratch_page);
> -			return PTR_ERR(vm->scratch_pdp);
> +			ret = PTR_ERR(vm->scratch_pdp);
> +			goto fail_pdp;
>  		}
>  	}
>  
> @@ -900,6 +900,20 @@ static int gen8_init_scratch(struct i915_address_space *vm)
>  		gen8_initialize_pdp(vm, vm->scratch_pdp);
>  
>  	return 0;
> +
> +fail_pdp:
> +	vm->scratch_pdp = NULL;

I don't think assigning to NULL is necessary. If this function fails,
it'll lead to driver init failure.

> +	free_pd(dev, vm->scratch_pd);
> +fail_pd:
> +	vm->scratch_pd = NULL;
> +	free_pt(dev, vm->scratch_pt);
> +fail_pt:
> +	vm->scratch_pt = NULL;
> +	free_scratch_page(dev, vm->scratch_page);
> +fail_scratch:
> +	vm->scratch_page = NULL;
> +

Same comment as in the last patch, related to labels, the label should
describe the code under goto section, not the code/situation that jumps
to it.

Regards, Joonas

> +	return ret;
>  }
>  
>  static int gen8_ppgtt_notify_vgt(struct i915_hw_ppgtt *ppgtt, bool create)
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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Re: [PATCH] drm/i915: tidy up gen8_init_scratch

[Dave Gordon]

On 26/04/16 10:27, Matthew Auld wrote:
> Use goto teardown path and also ensure we reset any struct members which
> would otherwise contain an error encoded pointer, and could be mistaken
> for a valid address.
>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_gem_gtt.c | 36 +++++++++++++++++++++++++-----------
>   1 file changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 0d666b3..a723b74 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -866,31 +866,31 @@ static void gen8_free_page_tables(struct drm_device *dev,
>   static int gen8_init_scratch(struct i915_address_space *vm)
>   {
>   	struct drm_device *dev = vm->dev;
> +	int ret;
>
>   	vm->scratch_page = alloc_scratch_page(dev);
> -	if (IS_ERR(vm->scratch_page))
> -		return PTR_ERR(vm->scratch_page);
> +	if (IS_ERR(vm->scratch_page)) {
> +		ret = PTR_ERR(vm->scratch_page);
> +		goto fail_scratch;
> +	}
>
>   	vm->scratch_pt = alloc_pt(dev);
>   	if (IS_ERR(vm->scratch_pt)) {
> -		free_scratch_page(dev, vm->scratch_page);
> -		return PTR_ERR(vm->scratch_pt);
> +		ret = PTR_ERR(vm->scratch_pt);
> +		goto fail_pt;
>   	}
>
>   	vm->scratch_pd = alloc_pd(dev);
>   	if (IS_ERR(vm->scratch_pd)) {
> -		free_pt(dev, vm->scratch_pt);
> -		free_scratch_page(dev, vm->scratch_page);
> -		return PTR_ERR(vm->scratch_pd);
> +		ret = PTR_ERR(vm->scratch_pd);
> +		goto fail_pd;
>   	}
>
>   	if (USES_FULL_48BIT_PPGTT(dev)) {
>   		vm->scratch_pdp = alloc_pdp(dev);
>   		if (IS_ERR(vm->scratch_pdp)) {
> -			free_pd(dev, vm->scratch_pd);
> -			free_pt(dev, vm->scratch_pt);
> -			free_scratch_page(dev, vm->scratch_page);
> -			return PTR_ERR(vm->scratch_pdp);
> +			ret = PTR_ERR(vm->scratch_pdp);
> +			goto fail_pdp;
>   		}
>   	}
>
> @@ -900,6 +900,20 @@ static int gen8_init_scratch(struct i915_address_space *vm)
>   		gen8_initialize_pdp(vm, vm->scratch_pdp);
>
>   	return 0;
> +
> +fail_pdp:
> +	vm->scratch_pdp = NULL;
> +	free_pd(dev, vm->scratch_pd);
> +fail_pd:
> +	vm->scratch_pd = NULL;
> +	free_pt(dev, vm->scratch_pt);
> +fail_pt:
> +	vm->scratch_pt = NULL;
> +	free_scratch_page(dev, vm->scratch_page);
> +fail_scratch:
> +	vm->scratch_page = NULL;
> +
> +	return ret;
>   }
>
>   static int gen8_ppgtt_notify_vgt(struct i915_hw_ppgtt *ppgtt, bool create)

Well, I agree it's a good idea not to assign non-NULL pointer values to 
members of an OUT parameter, but perhaps consider a strategy of 
assigning to a local, checking the result, and storing in the parameter 
block only after we know that it's a good pointer. Maybe even keep ALL 
the temporary pointers local and only assign *any* of them when we know 
we can assign *all* of them and return success. That way there's no 
cleanup of the result block required in the error path, only freeing of 
still-local values.

BTW, as it appears that this function can be called more than once in 
the lifetime of the driver, do we know that all these pointers will be 
NULL on entry? Even on the second and subsequent calls?

.Dave.
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Re: [PATCH] drm/i915: tidy up gen8_init_scratch

[Mika Kuoppala]

Dave Gordon <david.s.gordon@intel.com> writes:

> [ text/plain ]
> On 26/04/16 10:27, Matthew Auld wrote:
>> Use goto teardown path and also ensure we reset any struct members which
>> would otherwise contain an error encoded pointer, and could be mistaken
>> for a valid address.
>>
>> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
>> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_gem_gtt.c | 36 +++++++++++++++++++++++++-----------
>>   1 file changed, 25 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> index 0d666b3..a723b74 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> @@ -866,31 +866,31 @@ static void gen8_free_page_tables(struct drm_device *dev,
>>   static int gen8_init_scratch(struct i915_address_space *vm)
>>   {
>>   	struct drm_device *dev = vm->dev;
>> +	int ret;
>>
>>   	vm->scratch_page = alloc_scratch_page(dev);
>> -	if (IS_ERR(vm->scratch_page))
>> -		return PTR_ERR(vm->scratch_page);
>> +	if (IS_ERR(vm->scratch_page)) {
>> +		ret = PTR_ERR(vm->scratch_page);
>> +		goto fail_scratch;
>> +	}
>>
>>   	vm->scratch_pt = alloc_pt(dev);
>>   	if (IS_ERR(vm->scratch_pt)) {
>> -		free_scratch_page(dev, vm->scratch_page);
>> -		return PTR_ERR(vm->scratch_pt);
>> +		ret = PTR_ERR(vm->scratch_pt);
>> +		goto fail_pt;
>>   	}
>>
>>   	vm->scratch_pd = alloc_pd(dev);
>>   	if (IS_ERR(vm->scratch_pd)) {
>> -		free_pt(dev, vm->scratch_pt);
>> -		free_scratch_page(dev, vm->scratch_page);
>> -		return PTR_ERR(vm->scratch_pd);
>> +		ret = PTR_ERR(vm->scratch_pd);
>> +		goto fail_pd;
>>   	}
>>
>>   	if (USES_FULL_48BIT_PPGTT(dev)) {
>>   		vm->scratch_pdp = alloc_pdp(dev);
>>   		if (IS_ERR(vm->scratch_pdp)) {
>> -			free_pd(dev, vm->scratch_pd);
>> -			free_pt(dev, vm->scratch_pt);
>> -			free_scratch_page(dev, vm->scratch_page);
>> -			return PTR_ERR(vm->scratch_pdp);
>> +			ret = PTR_ERR(vm->scratch_pdp);
>> +			goto fail_pdp;
>>   		}
>>   	}
>>
>> @@ -900,6 +900,20 @@ static int gen8_init_scratch(struct i915_address_space *vm)
>>   		gen8_initialize_pdp(vm, vm->scratch_pdp);
>>
>>   	return 0;
>> +
>> +fail_pdp:
>> +	vm->scratch_pdp = NULL;
>> +	free_pd(dev, vm->scratch_pd);
>> +fail_pd:
>> +	vm->scratch_pd = NULL;
>> +	free_pt(dev, vm->scratch_pt);
>> +fail_pt:
>> +	vm->scratch_pt = NULL;
>> +	free_scratch_page(dev, vm->scratch_page);
>> +fail_scratch:
>> +	vm->scratch_page = NULL;
>> +
>> +	return ret;
>>   }
>>
>>   static int gen8_ppgtt_notify_vgt(struct i915_hw_ppgtt *ppgtt, bool create)
>
> Well, I agree it's a good idea not to assign non-NULL pointer values to 
> members of an OUT parameter, but perhaps consider a strategy of 
> assigning to a local, checking the result, and storing in the parameter 
> block only after we know that it's a good pointer. Maybe even keep ALL 
> the temporary pointers local and only assign *any* of them when we know 
> we can assign *all* of them and return success. That way there's no 
> cleanup of the result block required in the error path, only freeing of 
> still-local values.

Local would be clean but then it would be burden on the hot path.
Lets just incur the, now useless, writes on the error path.

>
> BTW, as it appears that this function can be called more than once in 
> the lifetime of the driver, do we know that all these pointers will be 
> NULL on entry? Even on the second and subsequent calls?
>

The defensive programming of is good, but in this case we
kzalloc the ppgtt, which contains the struct we are initializing.
If we are unsuccessful, we free the ppgtt. And the function is static
so there are no external users. 

That said, the value of separating the error handling into
a goto teardown is valuable for readability.

Change the goto labels as Joonas suggested and I am
ok with this.

Thanks,
-Mika

-
> .Dave.
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