[Q] mm/memblock.c: cast truncates bits from RED_INACTIVE

[Q] mm/memblock.c: cast truncates bits from RED_INACTIVE

[H Hartley Sweeten]

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Hello all,

Sparse is reporting a couple warnings in mm/memblock.c:

	warning: cast truncates bits from constant value (9f911029d74e35b becomes 9d74e35b)

The warnings are due to the cast of RED_INACTIVE in memblock_analyze():

	/* Check marker in the unused last array entry */
	WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base
		!= (phys_addr_t)RED_INACTIVE);
	WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base
		!= (phys_addr_t)RED_INACTIVE);

And in memblock_init():

	/* Write a marker in the unused last array entry */
	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;

Could this cause any problems?  If not, is there anyway to quiet the sparse noise?

Regards,
Hartley
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Re: [Q] mm/memblock.c: cast truncates bits from RED_INACTIVE

[Andrew Morton]

On Tue, 14 Jun 2011 19:47:19 -0500
H Hartley Sweeten <hartleys@visionengravers.com> wrote:

> Hello all,
> 
> Sparse is reporting a couple warnings in mm/memblock.c:
> 
> 	warning: cast truncates bits from constant value (9f911029d74e35b becomes 9d74e35b)
> 
> The warnings are due to the cast of RED_INACTIVE in memblock_analyze():
> 
> 	/* Check marker in the unused last array entry */
> 	WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base
> 		!= (phys_addr_t)RED_INACTIVE);
> 	WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base
> 		!= (phys_addr_t)RED_INACTIVE);
> 
> And in memblock_init():
> 
> 	/* Write a marker in the unused last array entry */
> 	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
> 	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
> 
> Could this cause any problems?  If not, is there anyway to quiet the sparse noise?
> 

It's all just a debugging check and that check will continue to work OK
despite this bug.

But yes, it's ugly and should be fixed.

I don't think that mm/memblock.c should have reused RED_INACTIVE. 
That's a slab thing and wedging it into a phys_addr_t was
inappropriate.

In fact I don't think RED_INACTIVE should exist.  It's just inviting
other subsystems to (ab)use it.  It should be replaced by a
slab-specific SLAB_RED_INACTIVE, as slub did with SLUB_RED_INACTIVE.


I'd suggest something like the below, which I didn't test.  Feel free to
send it back at me, or ignore it ;)


diff -puN include/linux/poison.h~a include/linux/poison.h
--- a/include/linux/poison.h~a
+++ a/include/linux/poison.h
@@ -40,6 +40,12 @@
 #define	RED_INACTIVE	0x09F911029D74E35BULL	/* when obj is inactive */
 #define	RED_ACTIVE	0xD84156C5635688C0ULL	/* when obj is active */
 
+#ifdef CONFIG_PHYS_ADDR_T_64BIT
+#define MEMBLOCK_INACTIVE	0x3a84fb0144c9e71bULL
+#else
+#define MEMBLOCK_INACTIVE	0x44c9e71bUL
+#endif
+
 #define SLUB_RED_INACTIVE	0xbb
 #define SLUB_RED_ACTIVE		0xcc
 
diff -puN mm/memblock.c~a mm/memblock.c
--- a/mm/memblock.c~a
+++ a/mm/memblock.c
@@ -758,9 +758,9 @@ void __init memblock_analyze(void)
 
 	/* Check marker in the unused last array entry */
 	WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base
-		!= (phys_addr_t)RED_INACTIVE);
+		!= MEMBLOCK_INACTIVE);
 	WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base
-		!= (phys_addr_t)RED_INACTIVE);
+		!= MEMBLOCK_INACTIVE);
 
 	memblock.memory_size = 0;
 
@@ -786,8 +786,8 @@ void __init memblock_init(void)
 	memblock.reserved.max	= INIT_MEMBLOCK_REGIONS;
 
 	/* Write a marker in the unused last array entry */
-	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
-	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
+	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE;
+	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE;
 
 	/* Create a dummy zero size MEMBLOCK which will get coalesced away later.
 	 * This simplifies the memblock_add() code below...
_

RE: [Q] mm/memblock.c: cast truncates bits from RED_INACTIVE

[H Hartley Sweeten]

On Monday, June 20, 2011 5:03 PM, Andrew Morton wrote:
> On Tue, 14 Jun 2011 19:47:19 -0500 H Hartley Sweeten wrote:
>
>> Hello all,
>> 
>> Sparse is reporting a couple warnings in mm/memblock.c:
>> 
>> 	warning: cast truncates bits from constant value (9f911029d74e35b becomes 9d74e35b)
>> 
>> The warnings are due to the cast of RED_INACTIVE in memblock_analyze():
>> 
>> 	/* Check marker in the unused last array entry */
>> 	WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base
>> 		!= (phys_addr_t)RED_INACTIVE);
>> 	WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base
>> 		!= (phys_addr_t)RED_INACTIVE);
>> 
>> And in memblock_init():
>> 
>> 	/* Write a marker in the unused last array entry */
>> 	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
>> 	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
>> 
>> Could this cause any problems?  If not, is there anyway to quiet the sparse noise?
>> 
>
> It's all just a debugging check and that check will continue to work OK
> despite this bug.
>
> But yes, it's ugly and should be fixed.
>
> I don't think that mm/memblock.c should have reused RED_INACTIVE. 
> That's a slab thing and wedging it into a phys_addr_t was
> inappropriate.
>
> In fact I don't think RED_INACTIVE should exist.  It's just inviting
> other subsystems to (ab)use it.  It should be replaced by a
> slab-specific SLAB_RED_INACTIVE, as slub did with SLUB_RED_INACTIVE.
>
>
> I'd suggest something like the below, which I didn't test.  Feel free to
> send it back at me, or ignore it ;)
>
>
> diff -puN include/linux/poison.h~a include/linux/poison.h
> --- a/include/linux/poison.h~a
> +++ a/include/linux/poison.h
> @@ -40,6 +40,12 @@
>  #define	RED_INACTIVE	0x09F911029D74E35BULL	/* when obj is inactive */
>  #define	RED_ACTIVE	0xD84156C5635688C0ULL	/* when obj is active */
>  
> +#ifdef CONFIG_PHYS_ADDR_T_64BIT
> +#define MEMBLOCK_INACTIVE	0x3a84fb0144c9e71bULL
> +#else
> +#define MEMBLOCK_INACTIVE	0x44c9e71bUL
> +#endif
> +
>  #define SLUB_RED_INACTIVE	0xbb
>  #define SLUB_RED_ACTIVE		0xcc
>  
> diff -puN mm/memblock.c~a mm/memblock.c
> --- a/mm/memblock.c~a
> +++ a/mm/memblock.c
> @@ -758,9 +758,9 @@ void __init memblock_analyze(void)
>  
>  	/* Check marker in the unused last array entry */
>  	WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base
> -		!= (phys_addr_t)RED_INACTIVE);
> +		!= MEMBLOCK_INACTIVE);
>  	WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base
> -		!= (phys_addr_t)RED_INACTIVE);
> +		!= MEMBLOCK_INACTIVE);
>  
>  	memblock.memory_size = 0;
>  
> @@ -786,8 +786,8 @@ void __init memblock_init(void)
>  	memblock.reserved.max	= INIT_MEMBLOCK_REGIONS;
>  
>  	/* Write a marker in the unused last array entry */
> -	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
> -	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
> +	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE;
> +	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE;
>  
>  	/* Create a dummy zero size MEMBLOCK which will get coalesced away later.
>  	 * This simplifies the memblock_add() code below...

FWIW, your patch above quiet's the sparse warnings on my system (arm ep93xx) and
the system boots and runs fine.

If you want it..

Tested-by: H Hartley Sweeten <hsweeten@visionengravers.com>

Re: [Q] mm/memblock.c: cast truncates bits from RED_INACTIVE

[Pekka Enberg]

On 6/21/11 3:31 AM, H Hartley Sweeten wrote:
> On Monday, June 20, 2011 5:03 PM, Andrew Morton wrote:
>> On Tue, 14 Jun 2011 19:47:19 -0500 H Hartley Sweeten wrote:
>>
>>> Hello all,
>>>
>>> Sparse is reporting a couple warnings in mm/memblock.c:
>>>
>>> 	warning: cast truncates bits from constant value (9f911029d74e35b becomes 9d74e35b)
>>>
>>> The warnings are due to the cast of RED_INACTIVE in memblock_analyze():
>>>
>>> 	/* Check marker in the unused last array entry */
>>> 	WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base
>>> 		!= (phys_addr_t)RED_INACTIVE);
>>> 	WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base
>>> 		!= (phys_addr_t)RED_INACTIVE);
>>>
>>> And in memblock_init():
>>>
>>> 	/* Write a marker in the unused last array entry */
>>> 	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
>>> 	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
>>>
>>> Could this cause any problems?  If not, is there anyway to quiet the sparse noise?
>>>
>>
>> It's all just a debugging check and that check will continue to work OK
>> despite this bug.
>>
>> But yes, it's ugly and should be fixed.
>>
>> I don't think that mm/memblock.c should have reused RED_INACTIVE.
>> That's a slab thing and wedging it into a phys_addr_t was
>> inappropriate.
>>
>> In fact I don't think RED_INACTIVE should exist.  It's just inviting
>> other subsystems to (ab)use it.  It should be replaced by a
>> slab-specific SLAB_RED_INACTIVE, as slub did with SLUB_RED_INACTIVE.
>>
>>
>> I'd suggest something like the below, which I didn't test.  Feel free to
>> send it back at me, or ignore it ;)
>>
>>
>> diff -puN include/linux/poison.h~a include/linux/poison.h
>> --- a/include/linux/poison.h~a
>> +++ a/include/linux/poison.h
>> @@ -40,6 +40,12 @@
>>   #define	RED_INACTIVE	0x09F911029D74E35BULL	/* when obj is inactive */
>>   #define	RED_ACTIVE	0xD84156C5635688C0ULL	/* when obj is active */
>>
>> +#ifdef CONFIG_PHYS_ADDR_T_64BIT
>> +#define MEMBLOCK_INACTIVE	0x3a84fb0144c9e71bULL
>> +#else
>> +#define MEMBLOCK_INACTIVE	0x44c9e71bUL
>> +#endif
>> +
>>   #define SLUB_RED_INACTIVE	0xbb
>>   #define SLUB_RED_ACTIVE		0xcc
>>
>> diff -puN mm/memblock.c~a mm/memblock.c
>> --- a/mm/memblock.c~a
>> +++ a/mm/memblock.c
>> @@ -758,9 +758,9 @@ void __init memblock_analyze(void)
>>
>>   	/* Check marker in the unused last array entry */
>>   	WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base
>> -		!= (phys_addr_t)RED_INACTIVE);
>> +		!= MEMBLOCK_INACTIVE);
>>   	WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base
>> -		!= (phys_addr_t)RED_INACTIVE);
>> +		!= MEMBLOCK_INACTIVE);
>>
>>   	memblock.memory_size = 0;
>>
>> @@ -786,8 +786,8 @@ void __init memblock_init(void)
>>   	memblock.reserved.max	= INIT_MEMBLOCK_REGIONS;
>>
>>   	/* Write a marker in the unused last array entry */
>> -	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
>> -	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE;
>> +	memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE;
>> +	memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE;
>>
>>   	/* Create a dummy zero size MEMBLOCK which will get coalesced away later.
>>   	 * This simplifies the memblock_add() code below...
>
> FWIW, your patch above quiet's the sparse warnings on my system (arm ep93xx) and
> the system boots and runs fine.
>
> If you want it..
>
> Tested-by: H Hartley Sweeten<hsweeten@visionengravers.com>

Acked-by: Pekka Enberg <penberg@kernel.org>