From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IdejeKfu" Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1D057D5C for ; Wed, 6 Dec 2023 13:02:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1701896533; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yHW20tuEOrmNp4P41P/HLfeGuZPZFZ5btUUMCBjAyAo=; b=IdejeKfuAmbLBWE992qTb78Bjo78t/JICzCeIt1W3H1eVbpj22YscQhKT6NjvOajmRzxfv BXb/1jMEWw0cv3XqZP5HoS4UU5EM+w+YiCN73qXvjjZzr5ifdXaOadiQGz7Cy3+HRrxPHF YUVoc7xkOxwguaRKYJKh/xrNIztQASs= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-58-Tr0n8Aj5Or-lbiOYGgyS8w-1; Wed, 06 Dec 2023 16:02:07 -0500 X-MC-Unique: Tr0n8Aj5Or-lbiOYGgyS8w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A252F8353F2; Wed, 6 Dec 2023 21:02:04 +0000 (UTC) Received: from [10.22.34.92] (unknown [10.22.34.92]) by smtp.corp.redhat.com (Postfix) with ESMTP id B2EEB111E404; Wed, 6 Dec 2023 21:02:02 +0000 (UTC) Message-ID: <469f44fb-2371-4b3b-bc1c-d09ec35a5ec8@redhat.com> Date: Wed, 6 Dec 2023 16:02:02 -0500 Precedence: bulk X-Mailing-List: linux-leds@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 01/10] devm-helpers: introduce devm_mutex_init Content-Language: en-US To: Hans de Goede , George Stark , pavel@ucw.cz, lee@kernel.org, vadimp@nvidia.com, mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, mazziesaccount@gmail.com, andy.shevchenko@gmail.com, jic23@kernel.org, peterz@infradead.org Cc: linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kernel@salutedevices.com References: <20231204180603.470421-1-gnstark@salutedevices.com> <20231204180603.470421-2-gnstark@salutedevices.com> <81798fe5-f89e-482f-b0d0-674ccbfc3666@redhat.com> <29584eb6-fa10-4ce0-9fa3-0c409a582445@salutedevices.com> <580ecff0-b335-4cc0-b928-a99fe73741ca@redhat.com> From: Waiman Long In-Reply-To: <580ecff0-b335-4cc0-b928-a99fe73741ca@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 On 12/6/23 14:55, Hans de Goede wrote: > Hi, > > On 12/6/23 19:58, George Stark wrote: >> Hello Hans >> >> Thanks for the review. >> >> On 12/6/23 18:01, Hans de Goede wrote: >>> Hi George, >>> >>> On 12/4/23 19:05, George Stark wrote: >>>> Using of devm API leads to certain order of releasing resources. >>>> So all dependent resources which are not devm-wrapped should be deleted >>>> with respect to devm-release order. Mutex is one of such objects that >>>> often is bound to other resources and has no own devm wrapping. >>>> Since mutex_destroy() actually does nothing in non-debug builds >>>> frequently calling mutex_destroy() is just ignored which is safe for now >>>> but wrong formally and can lead to a problem if mutex_destroy() is >>>> extended so introduce devm_mutex_init(). >>>> >>>> Signed-off-by: George Stark >>>> --- >>>>   include/linux/devm-helpers.h | 18 ++++++++++++++++++ >>>>   1 file changed, 18 insertions(+) >>>> >>>> diff --git a/include/linux/devm-helpers.h b/include/linux/devm-helpers.h >>>> index 74891802200d..2f56e476776f 100644 >>>> --- a/include/linux/devm-helpers.h >>>> +++ b/include/linux/devm-helpers.h >>>> @@ -76,4 +76,22 @@ static inline int devm_work_autocancel(struct device *dev, >>>>       return devm_add_action(dev, devm_work_drop, w); >>>>   } >>>>   +static inline void devm_mutex_release(void *res) >>>> +{ >>>> +    mutex_destroy(res); >>>> +} >>>> + >>>> +/** >>>> + * devm_mutex_init - Resource-managed mutex initialization >>>> + * @dev:    Device which lifetime work is bound to >>>> + * @lock:    Pointer to a mutex >>>> + * >>>> + * Initialize mutex which is automatically destroyed when driver is detached. >>>> + */ >>>> +static inline int devm_mutex_init(struct device *dev, struct mutex *lock) >>>> +{ >>>> +    mutex_init(lock); >>>> +    return devm_add_action_or_reset(dev, devm_mutex_release, lock); >>>> +} >>>> + >>>>   #endif >>> mutex_destroy() only actually does anything if CONFIG_DEBUG_MUTEXES >>> is set, otherwise it is an empty inline-stub. >>> >>> Adding a devres resource to the device just to call an empty inline >>> stub which is a no-op seems like a waste of resources. IMHO it >>> would be better to change this to: >>> >>> static inline int devm_mutex_init(struct device *dev, struct mutex *lock) >>> { >>>     mutex_init(lock); >>> #ifdef CONFIG_DEBUG_MUTEXES >>>     return devm_add_action_or_reset(dev, devm_mutex_release, lock); >>> #else >>>     return 0; >>> #endif >>> } >>> >>> To avoid the unnecessary devres allocation when >>> CONFIG_DEBUG_MUTEXES is not set. >> Honestly saying I don't like unnecessary devres allocation either but the proposed approach has its own price: >> >> 1) we'll have more than one place with branching if mutex_destroy is empty or not using  indirect condition. If suddenly mutex_destroy is extended for non-debug code (in upstream branch or e.g. by someone for local debug) than there'll be a problem. >> >> 2) If mutex_destroy is empty or not depends on CONFIG_PREEMPT_RT option too. When CONFIG_PREEMPT_RT is on mutex_destroy is always empty. >> >> As I see it only the mutex interface (mutex.h) has to say definitely if mutex_destroy must be called. Probably we could add some define to include/linux/mutex.h,like IS_MUTEX_DESTROY_REQUIRED and declare it near mutex_destroy definition itself. > That (a IS_MUTEX_DESTROY_REQUIRED define) is an interesting idea. Lets see for v3 if the mutex maintainers will accept that and if not then I guess we will just need to live with the unnecessary devres allocation. The purpose of calling mutex_destroy() is to mark a mutex as being destroyed so that any subsequent call to mutex_lock/unlock will cause a warning to be printed when CONFIG_DEBUG_MUTEXES is defined. I would not say that mutex_destroy() is required. Rather it is a nice to have for catching programming error. Cheers, Longman