[PATCH] kmalloc: Return NULL instead of link failure

[PATCH] kmalloc: Return NULL instead of link failure

[Jeff Mahoney]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

 The SLAB kmalloc with a constant value isn't consistent with the other
 implementations because it bails out with __you_cannot_kmalloc_that_much
 rather than returning NULL and properly allowing the caller to fall back
 to vmalloc or take other action. This doesn't happen with a non-constant
 value or with SLOB or SLUB.

 Starting with 2.6.28, I've been seeing build failures on s390x. This is
 due to init_section_page_cgroup trying to allocate 2.5MB when the max
 size for a kmalloc on s390x is 2MB.

 It's failing because the value is constant. The workarounds at the call
 size are ugly and the caller shouldn't have to change behavior depending
 on what the backend of the API is.

 So, this patch eliminates the link failure and returns NULL like the
 other implementations.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
- ---
 include/linux/slab_def.h |   10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

- --- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -43,10 +43,7 @@ static inline void *kmalloc(size_t size,
 			i++;
 #include <linux/kmalloc_sizes.h>
 #undef CACHE
- -		{
- -			extern void __you_cannot_kmalloc_that_much(void);
- -			__you_cannot_kmalloc_that_much();
- -		}
+		return NULL;
 found:
 #ifdef CONFIG_ZONE_DMA
 		if (flags & GFP_DMA)
@@ -77,10 +74,7 @@ static inline void *kmalloc_node(size_t
 			i++;
 #include <linux/kmalloc_sizes.h>
 #undef CACHE
- -		{
- -			extern void __you_cannot_kmalloc_that_much(void);
- -			__you_cannot_kmalloc_that_much();
- -		}
+		return NULL;
 found:
 #ifdef CONFIG_ZONE_DMA
 		if (flags & GFP_DMA)

- -- 
Jeff Mahoney
SUSE Labs
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.9 (GNU/Linux)
Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org

iEYEARECAAYFAkl183YACgkQLPWxlyuTD7IMnQCfbf4NvJuyTustFrdJD/lcl6ub
QQ0AniWOsKCWnBWuLLnm6rM+Atq6LBfd
=/evL
-----END PGP SIGNATURE-----

Re: [PATCH] kmalloc: Return NULL instead of link failure

[Andrew Morton]

On Tue, 20 Jan 2009 10:53:26 -0500
Jeff Mahoney <jeffm@suse.com> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
>  The SLAB kmalloc with a constant value isn't consistent with the other
>  implementations because it bails out with __you_cannot_kmalloc_that_much
>  rather than returning NULL and properly allowing the caller to fall back
>  to vmalloc or take other action. This doesn't happen with a non-constant
>  value or with SLOB or SLUB.
> 
>  Starting with 2.6.28, I've been seeing build failures on s390x. This is
>  due to init_section_page_cgroup trying to allocate 2.5MB when the max
>  size for a kmalloc on s390x is 2MB.
> 
>  It's failing because the value is constant. The workarounds at the call
>  size are ugly and the caller shouldn't have to change behavior depending
>  on what the backend of the API is.
> 
>  So, this patch eliminates the link failure and returns NULL like the
>  other implementations.
> 

OK by me, is that's what the other sl[abcd...xyz]b.c implementations
do.

That __you_cannot_kmalloc_that_much() thing has frequently been a PITA
anyway - some gcc versions flub the constant_p() test and end up
referencing __you_cannot_kmalloc_that_much() when the callsite was
passing a variable `size' arg.

> - ---
>  include/linux/slab_def.h |   10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> - --- a/include/linux/slab_def.h
> +++ b/include/linux/slab_def.h
> @@ -43,10 +43,7 @@ static inline void *kmalloc(size_t size,
>  			i++;
>  #include <linux/kmalloc_sizes.h>
>  #undef CACHE
> - -		{
> - -			extern void __you_cannot_kmalloc_that_much(void);
> - -			__you_cannot_kmalloc_that_much();
> - -		}
> +		return NULL;
>  found:
>  #ifdef CONFIG_ZONE_DMA
>  		if (flags & GFP_DMA)
> @@ -77,10 +74,7 @@ static inline void *kmalloc_node(size_t
>  			i++;
>  #include <linux/kmalloc_sizes.h>
>  #undef CACHE
> - -		{
> - -			extern void __you_cannot_kmalloc_that_much(void);
> - -			__you_cannot_kmalloc_that_much();
> - -		}
> +		return NULL;
>  found:
>  #ifdef CONFIG_ZONE_DMA
>  		if (flags & GFP_DMA)
> 

Strange patch format, but it applied.

I'll punt this patch in the Pekka direction.

Do you think we should include it in 2.6.28.x?

Re: [PATCH] kmalloc: Return NULL instead of link failure

[Jeff Mahoney]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Andrew Morton wrote:
> Strange patch format, but it applied.

Ugh, sorry about that. I forgot to disable the GPG signing. It escapes
- -'s like that.

> I'll punt this patch in the Pekka direction.
> 
> Do you think we should include it in 2.6.28.x?

I think so. It's a corner case, but does fix a build failure.

- -Jeff

- --
Jeff Mahoney
SUSE Labs
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.9 (GNU/Linux)
Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org

iEYEARECAAYFAkl/gCcACgkQLPWxlyuTD7IdcwCgkdOmH3P8a9q1RQYsOcCkG8C0
TYsAn3rEJMROguhVqbWuFlzg58t+vVEL
=RM/e
-----END PGP SIGNATURE-----

Re: [PATCH] kmalloc: Return NULL instead of link failure

[Pekka Enberg]

Andrew Morton wrote:
> On Tue, 20 Jan 2009 10:53:26 -0500
> Jeff Mahoney <jeffm@suse.com> wrote:
> 
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>>  The SLAB kmalloc with a constant value isn't consistent with the other
>>  implementations because it bails out with __you_cannot_kmalloc_that_much
>>  rather than returning NULL and properly allowing the caller to fall back
>>  to vmalloc or take other action. This doesn't happen with a non-constant
>>  value or with SLOB or SLUB.
>>
>>  Starting with 2.6.28, I've been seeing build failures on s390x. This is
>>  due to init_section_page_cgroup trying to allocate 2.5MB when the max
>>  size for a kmalloc on s390x is 2MB.
>>
>>  It's failing because the value is constant. The workarounds at the call
>>  size are ugly and the caller shouldn't have to change behavior depending
>>  on what the backend of the API is.
>>
>>  So, this patch eliminates the link failure and returns NULL like the
>>  other implementations.
>>
> 
> OK by me, is that's what the other sl[abcd...xyz]b.c implementations
> do.
> 
> That __you_cannot_kmalloc_that_much() thing has frequently been a PITA
> anyway - some gcc versions flub the constant_p() test and end up
> referencing __you_cannot_kmalloc_that_much() when the callsite was
> passing a variable `size' arg.

[snip]

> Strange patch format, but it applied.
> 
> I'll punt this patch in the Pekka direction.

Applied, thanks!

		Pekka