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="aEzYpIoK" 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 DE8C55270 for ; Thu, 7 Dec 2023 13:29:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1701984571; 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=Qe0P0o7yRkTD2fUSOfyBoEKZezhrInTjx41nrGxtbwk=; b=aEzYpIoKojqx38Vyc9o13thPzOc6FqW62IHAr6yEQnJ6l+fiTb4GLV6dqpMUkFeuCVCHv4 3txnEhfVrxmkEYZyeuaXqTWKUTAv3FHvy7Rfa1O8enXCGmRFLsUWn3NQ3TjheYblolGNaN V9GsyNmKj/FADnohifgJewmd7s/aJJ8= 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-125-Yytt9uJcMF21fHVxfcxU3A-1; Thu, 07 Dec 2023 16:29:25 -0500 X-MC-Unique: Yytt9uJcMF21fHVxfcxU3A-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (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 AB9E210C04E9; Thu, 7 Dec 2023 21:29:24 +0000 (UTC) Received: from [10.22.32.209] (unknown [10.22.32.209]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1BA518174; Thu, 7 Dec 2023 21:29:23 +0000 (UTC) Message-ID: <3407893a-3ede-4755-9b64-c0c2c9108f77@redhat.com> Date: Thu, 7 Dec 2023 16:29:22 -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 From: Waiman Long 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> <469f44fb-2371-4b3b-bc1c-d09ec35a5ec8@redhat.com> In-Reply-To: <469f44fb-2371-4b3b-bc1c-d09ec35a5ec8@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 On 12/6/23 16:02, 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, >>>> >>>> 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. OTOH, one thing that we can probably do in mutex.h is something like diff --git a/include/linux/mutex.h b/include/linux/mutex.h index a33aa9eb9fc3..7db7862de3f1 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -83,6 +83,9 @@ struct mutex {  extern void mutex_destroy(struct mutex *lock); +/* mutex_destroy() is a real function, not a NOP */ +#define mutex_destroy  mutex_destroy +  #else ---------------------------------------- Now in some devm files, you can use the absense/presence of mutex_destroy macro to decide on what to do. Cheers, Longman