Re: [PATCH] treewide: Replace kmalloc with kmalloc_obj for non-scalar types

[Guenter Roeck]

On Fri, Feb 20, 2026 at 11:49:23PM -0800, Kees Cook wrote:
> This is the result of running the Coccinelle script from
> scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
> avoid scalar types (which need careful case-by-case checking), and
> instead replace kmalloc-family calls that allocate struct or union
> object instances:
> 
> Single allocations:	kmalloc(sizeof(TYPE), ...)
> are replaced with:	kmalloc_obj(TYPE, ...)
> 
> Array allocations:	kmalloc_array(COUNT, sizeof(TYPE), ...)
> are replaced with:	kmalloc_objs(TYPE, COUNT, ...)
> 
> Flex array allocations:	kmalloc(struct_size(PTR, FAM, COUNT), ...)
> are replaced with:	kmalloc_flex(*PTR, FAM, COUNT, ...)
> 
> (where TYPE may also be *VAR)
> 
> The resulting allocations no longer return "void *", instead returning
> "TYPE *".
> 
> Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
> ---
> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
> index 37455e74d314..42f392e6add3 100644
> --- a/arch/um/drivers/ubd_kern.c
> +++ b/arch/um/drivers/ubd_kern.c
> @@ -1069,20 +1069,16 @@ static int __init ubd_init(void)
>  	if (register_blkdev(UBD_MAJOR, "ubd"))
>  		return -1;
>  
> -	irq_req_buffer = kmalloc_array(UBD_REQ_BUFFER_SIZE,
> -				       sizeof(struct io_thread_req *),
> -				       GFP_KERNEL
> -		);
> +	irq_req_buffer = kmalloc_objs(struct io_thread_req *,
> +				      UBD_REQ_BUFFER_SIZE, GFP_KERNEL);
>  	irq_remainder = 0;
>  
>  	if (irq_req_buffer == NULL) {
>  		printk(KERN_ERR "Failed to initialize ubd buffering\n");
>  		return -ENOMEM;
>  	}
> -	io_req_buffer = kmalloc_array(UBD_REQ_BUFFER_SIZE,
> -				      sizeof(struct io_thread_req *),
> -				      GFP_KERNEL
> -		);
> +	io_req_buffer = kmalloc_objs(struct io_thread_req *,
> +				     UBD_REQ_BUFFER_SIZE, GFP_KERNEL);

Building um:defconfig ... failed
--------------
Error log:
arch/um/drivers/ubd_kern.c: In function 'ubd_init':
arch/um/drivers/ubd_kern.c:1072:24: error: assignment to 'struct io_thread_req * (*)[]' from incompatible pointer type 'struct io_thread_req **' [-Wincompatible-pointer-types]
 1072 |         irq_req_buffer = kmalloc_objs(struct io_thread_req *,
      |                        ^
arch/um/drivers/ubd_kern.c:1080:23: error: assignment to 'struct io_thread_req * (*)[]' from incompatible pointer type 'struct io_thread_req **' [-Wincompatible-pointer-types]
 1080 |         io_req_buffer = kmalloc_objs(struct io_thread_req *,

Guenter