Re: [PATCH v4] gpio: sim: fix an invalid __free() usage

[Linus Torvalds]

On Tue, 19 Sept 2023 at 03:49, Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> Nope, k*alloc*() returns ZERO or NULL on failure. That's what most developers
> are missing :-)

Absolutely not.

k*alloc() returns NULL on failure. Absolutely nothing else.

On *success*, it can return the special ZERO_SIZE_PTR. But that is
*not* a failure at all. It's very much a successful pointer.

Now, it's a pointer that you can't actually dereference, but that's
very much intentional. You can't dereference it, because you asked for
a zero-sized allocation. You got a zero-sized allocation.

But please never *ever* think it's a failure. It's very much not a
failure case, and it is very much intentional.

It's different from NULL exactly *because* it's successful, and
exactly so that you can write

     ptr = kmalloc(size);
     if (!ptr)
          return -ENOMEM;

without having to worry about the "size is zero" case.

The standard user-space "malloc()" library is misdesigned. Surprise
surprise. The kernel isn't.

                Linus