linux-kernel - RE: [PATCH] cleanup: Add usage and style documentation

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Date: Sat, 23 Mar 2024 19:01:03 +0100
From: Markus Elfring <Markus.Elfring@....de>
To: Dan Williams <dan.j.williams@...el.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 kernel-janitors@...r.kernel.org
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Ira Weiny <ira.weiny@...el.com>,
 Jesse Brandeburg <jesse.brandeburg@...el.com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Julia Lawall <Julia.Lawall@...ia.fr>, Kevin Tian <kevin.tian@...el.com>,
 Lukas Wunner <lukas.wunner@...el.com>
Subject: RE: [PATCH] cleanup: Add usage and style documentation

> 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