RE: [PATCH] cleanup: Add usage and style documentation

From: Markus Elfring <Markus.Elfring@web.de>
To: Dan Williams <dan.j.williams@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, kernel-janitors@vger.kernel.org
Cc: "Bjorn Helgaas" <bhelgaas@google.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
	"Ira Weiny" <ira.weiny@intel.com>,
	"Jesse Brandeburg" <jesse.brandeburg@intel.com>,
	"Jonathan Cameron" <Jonathan.Cameron@huawei.com>,
	"Julia Lawall" <Julia.Lawall@inria.fr>,
	"Kevin Tian" <kevin.tian@intel.com>,
	"Lukas Wunner" <lukas.wunner@intel.com>
Subject: RE: [PATCH] cleanup: Add usage and style documentation
Date: Sat, 23 Mar 2024 19:01:03 +0100	[thread overview]
Message-ID: <f3849725-b7b3-4edc-8220-aabeb79b8151@web.de> (raw)
In-Reply-To: <65fe1f9aadf51_2690d2948f@dwillia2-mobl3.amr.corp.intel.com.notmuch>

> DEFINE_FREE(remove_free, struct object *, if (_T) remove_free(_T))
> static int init(void)
> {
>         struct object *obj __free(remove_free) = NULL;
>         int err;
>
>         guard(mutex)(lock);
>         obj = alloc_add();
>
>         if (!obj)
>                 return -ENOMEM;
>
>         err = other_init(obj);
>         if (err)
>                 return err; // remove_free() called without the lock!!
>
>         no_free_ptr(obj);
>         return 0;
> }

You demonstrated an improvable lock granularity and a questionable combination
of variable scopes.

> The fix for this bug is to replace the "__free(...) = NULL" pattern and
> move the assignment to the declaration.
>
>         guard(mutex)(lock);
>         struct object *obj __free(remove_free) = alloc_add();

How do you think about to describe such a source code transformation
as a conversion of a variable assignment to a variable definition
at the place of a resource allocation?

Would you like to increase the collaboration with the macros “DEFINE_CLASS” and “CLASS”?
https://elixir.bootlin.com/linux/v6.8.1/source/include/linux/cleanup.h#L82

Regards,
Markus