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Message-ID: <CAHk-=wgK+PimVukScvVjoqOdOWWG_e+xCurhP_9SvA_+7scYWw@mail.gmail.com>
Date: Sat, 23 Sep 2023 11:19:08 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: brgl@...ev.pl, Linus Walleij <linus.walleij@...aro.org>,
Kent Gibson <warthog618@...il.com>,
Alexey Dobriyan <adobriyan@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
akpm@...ux-foundation.org, linux-gpio@...r.kernel.org,
linux-kernel@...r.kernel.org,
Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v4] gpio: sim: fix an invalid __free() usage
On Tue, 19 Sept 2023 at 03:49, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> 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
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