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="ZazC0Vo4" Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E03C1D6D for ; Wed, 6 Dec 2023 18:16:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1701915405; 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=hBSYHwojXw9kaGuT0KXDyW/rgXDL9EP6Xo6RAZZVUjw=; b=ZazC0Vo4Y591Zm0a4/k3lN0Aq0FJG1ULOZIB4zog7hZPx+Jl6f5CuGv0NOfVohDxRPRg5N C8Uibigf/uP6WbWCYiSDZ8YESc3fF4T0lotQYpt2Y4ZXL01iM+5xtEPnRo9rJ+OFPz/tJe TeGOzGjNITTKLeqQx6pmFqJBm8Ytce8= 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-471-rmphrsgtOkS3HsEJKlrQog-1; Wed, 06 Dec 2023 21:16:38 -0500 X-MC-Unique: rmphrsgtOkS3HsEJKlrQog-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (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 EA08F101A551; Thu, 7 Dec 2023 02:16:37 +0000 (UTC) Received: from [10.22.34.92] (unknown [10.22.34.92]) by smtp.corp.redhat.com (Postfix) with ESMTP id 766B4C15E6C; Thu, 7 Dec 2023 02:16:35 +0000 (UTC) Message-ID: <377e4437-7051-4d88-ae68-1460bcd692e1@redhat.com> Date: Wed, 6 Dec 2023 21:16:35 -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: George Stark , Hans de Goede , 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, boqun.feng@gmail.com, will@kernel.org, mingo@redhat.com 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> <469f44fb-2371-4b3b-bc1c-d09ec35a5ec8@redhat.com> <75368bdb-b54e-4e15-a3c0-89b920e5e729@salutedevices.com> From: Waiman Long In-Reply-To: <75368bdb-b54e-4e15-a3c0-89b920e5e729@salutedevices.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.8 On 12/6/23 19:37, George Stark wrote: > Hello Waiman > > Thanks for the review. > > On 12/7/23 00:02, Waiman Long wrote: >> 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, >>>>> > ... >>>>> 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 s> >>>>> 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 >>>>> } >>>>> ee 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. > > This is quite understandable but probably mutex_destroy() is not the > best name for an optional API. Questions are asked over and over again > if it can be safely ignored taking into account that it could be > extended in the future. Every maintainer makes decision on that question > in his own way and it leads to inconsistency. > > devm_mutex_init could take responsibility for calling/dropping > mutex_destroy() on its own. The DEBUG_MUTEXES code is relatively old and there was no major change to it for a number of years. I don't see we will make major change to it in the near future. Of course, thing may change if there are new requirement that may affect the DEBUG_MUTEXES code. Cheers, Longman > >> Cheers, >> Longman >> >