linux-kernel - Re: Buggy __free(kfree) usage pattern already in tree

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Date:   Fri, 15 Sep 2023 23:32:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        akpm@...ux-foundation.org
Subject: Re: Buggy __free(kfree) usage pattern already in tree

On Fri, Sep 15, 2023 at 02:22:02PM -0700, Linus Torvalds wrote:

> Naming is hard, let's not make it worse by making it actively misleading.

I actually did use the DEFINE_FREE() helper, will go fix. Because yes,
free is not the right word in this case.

> And honestly, I think the above is actually a *HORIBLE* argument for
> doing that "initialize to NULL, change later". I think the above is
> exactly the kind of code that we ABSOLUTELY DO NOT WANT.
> 
> You should aim for a nice
> 
>         struct rw_semaphore *struct rw_semaphore *exec_update_lock
>             __cleanup(release_exec_update_lock) = get_exec_update_lock(task);

Ah, that might be nicer still than the class thing I proposed in a
follow up email.

It also got me thinking about named_guard() for the myriad of
conditional locks we have.

	named_guard(try_mutex, foo_guard)(&foo->lock);
	if (foo_guard) {
		// we got the lock, do our thing
	}


or

	named_guard(interruptible_mutex, foo_guard)(&foo->lock);
	if (!foo_guard)
		return -EINTR;


Are these sane patterns?