Received-SPF: pass (google.com: domain of linux-kernel+bounces-77150-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Message-ID: <7013bf9e-2663-4613-ae61-61872e81355b@redhat.com>
Date: Thu, 22 Feb 2024 19:33:15 +0100
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH 1/2] devm-helpers: Add resource managed version of mutex
 init
To: Matthew Auld <matthew.auld@intel.com>, =?UTF-8?Q?Marek_Beh=C3=BAn?=
 <kabel@kernel.org>, linux-kernel@vger.kernel.org,
 Matti Vaittinen <mazziesaccount@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
 Bartosz Golaszewski <brgl@bgdev.pl>,
 Lucas De Marchi <lucas.demarchi@intel.com>, Oded Gabbay
 <ogabbay@kernel.org>, =?UTF-8?Q?Thomas_Hellstr=C3=B6m?=
 <thomas.hellstrom@linux.intel.com>,
 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
 Maxime Ripard <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>,
 David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
 Aleksandr Mezin <mezin.alexander@gmail.com>, Jean Delvare
 <jdelvare@suse.com>, Guenter Roeck <linux@roeck-us.net>,
 Pavel Machek <pavel@ucw.cz>, Lee Jones <lee@kernel.org>,
 Sebastian Reichel <sre@kernel.org>, Matthias Brugger
 <matthias.bgg@gmail.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>,
 linux-gpio@vger.kernel.org, intel-xe@lists.freedesktop.org,
 dri-devel@lists.freedesktop.org, linux-hwmon@vger.kernel.org,
 linux-leds@vger.kernel.org, linux-pm@vger.kernel.org,
 linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org
References: <20240222145838.12916-1-kabel@kernel.org>
 <03e62bcf-137c-4947-8f34-0cbfcba92a30@intel.com>
Content-Language: en-US, nl
From: Hans de Goede <hdegoede@redhat.com>
In-Reply-To: <03e62bcf-137c-4947-8f34-0cbfcba92a30@intel.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Hi,

On 2/22/24 17:44, Matthew Auld wrote:
> On 22/02/2024 14:58, Marek Behún wrote:
>> A few drivers are doing resource-managed mutex initialization by
>> implementing ad-hoc one-liner mutex dropping functions and using them
>> with devm_add_action_or_reset(). Help drivers avoid these repeated
>> one-liners by adding managed version of mutex initialization.

<snip>

>> index 74891802200d..70640fb96117 100644
>> --- a/include/linux/devm-helpers.h
>> +++ b/include/linux/devm-helpers.h
>> @@ -24,6 +24,8 @@
>>    */
>>     #include <linux/device.h>
>> +#include <linux/kconfig.h>
>> +#include <linux/mutex.h>
>>   #include <linux/workqueue.h>
>>     static inline void devm_delayed_work_drop(void *res)
>> @@ -76,4 +78,34 @@ static inline int devm_work_autocancel(struct device *dev,
>>       return devm_add_action(dev, devm_work_drop, w);
>>   }
>>   +static inline void devm_mutex_drop(void *res)
>> +{
>> +    mutex_destroy(res);
>> +}
>> +
>> +/**
>> + * devm_mutex_init - Resource managed mutex initialization
>> + * @dev:    Device which lifetime mutex is bound to
>> + * @lock:    Mutex to be initialized (and automatically destroyed)
>> + *
>> + * Initialize mutex which is automatically destroyed when driver is detached.
>> + * A few drivers initialize mutexes which they want destroyed before driver is
>> + * detached, for debugging purposes.
>> + * devm_mutex_init() can be used to omit the explicit mutex_destroy() call when
>> + * driver is detached.
>> + */
>> +static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
>> +{
>> +    mutex_init(lock);
> 
> Do you know if this this needs __always_inline? The static lockdep key in mutex_init() should be
> different for each caller class. See c21f11d182c2 ("drm: fix drmm_mutex_init()").

That is a very good point. I believe that this should mirror mutex_init() and
the actual static inline function should be __devm_mutex_init() which takes
the key as extra argument (and calls __mutex_init()) and then make
devm_mutex_init() itself a macro mirroring the mutex_init() macro.

Regards,

Hans


> 
>> +
>> +    /*
>> +     * mutex_destroy() is an empty function if CONFIG_DEBUG_MUTEXES is
>> +     * disabled. No need to allocate an action in that case.
>> +     */
>> +    if (IS_ENABLED(CONFIG_DEBUG_MUTEXES))
>> +        return devm_add_action_or_reset(dev, devm_mutex_drop, lock);
>> +    else
>> +        return 0;
>> +}
>> +
>>   #endif
>