mm/slab_common: Improve error handling in kmem_cache_create

mm/slab_common: Improve error handling in kmem_cache_create

Instead of using s == NULL use an errorcode. This allows much more
detailed diagnostics as to what went wrong. As we add more functionality
from the slab allocators to the common kmem_cache_create() function we will
also add more error conditions.

Print the error code during the panic as well as in a warning if the module
can handle failure. The API for kmem_cache_create() currently does not allow
the returning of an error code. Return NULL but log the cause of the problem
in the syslog.

Reviewed-by: Glauber Costa <[email protected]>
Acked-by: David Rientjes <[email protected]>
Signed-off-by: Christoph Lameter <[email protected]>
Signed-off-by: Pekka Enberg <[email protected]>