Re: [PATCH v5] mm, slab: Check GFP_SLAB_BUG_MASK before alloc_pages in kmalloc_order

[Matthew Wilcox <willy@infradead.org>]

On Sat, Jul 04, 2020 at 02:26:07AM +0000, Long Li wrote:
> kmalloc cannot allocate memory from HIGHMEM.  Allocating large amounts
> of memory currently bypasses the check and will simply leak the memory
> when page_address() returns NULL.  To fix this, factor the
> GFP_SLAB_BUG_MASK check out of slab & slub, and call it from
> kmalloc_order() as well. In order to make the code clear, the warning
> message is put in one place.
> 
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Pekka Enberg <penberg@kernel.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Long Li <lonuxli.64@gmail.com>
> ---
> 
> changes in v5:
> -Change the check function name to kmalloc_fix_flags(), This name
> may be more appropriate.
> 
> changes in V4:
> -Change the check function name to kmalloc_check_flags()
> -Put the flags check into the kmalloc_check_flags()

No.  As I said:

The point of not doing that was that this is unlikely().  With your
change there is now a function call to check something that's (extremely)
unlikely().