From mboxrd@z Thu Jan 1 00:00:00 1970 From: arvindY Subject: Re: [PATCH] PM / devfreq: use put_device() instead of kfree() Date: Fri, 13 Apr 2018 07:45:39 +0530 Message-ID: <5AD012CB.7030003@gmail.com> References: <5AD001C5.2040406@samsung.com> <5AD0041D.2050506@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <5AD0041D.2050506@samsung.com> Sender: linux-kernel-owner@vger.kernel.org To: Chanwoo Choi , myungjoo.ham@samsung.com, kyungmin.park@samsung.com Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org List-Id: linux-pm@vger.kernel.org Hi Chanwoo, On Friday 13 April 2018 06:43 AM, Chanwoo Choi wrote: > On 2018년 04월 13일 10:03, Chanwoo Choi wrote: >> Hi, >> >> I'm sorry for the late reply. >> >> On 2018년 03월 30일 20:44, Arvind Yadav wrote: >>> Never directly free @dev after calling device_register() or >>> device_unregister(), even if device_register() returned an error. >>> Always use put_device() to give up the reference initialized. >>> >>> Signed-off-by: Arvind Yadav >>> --- >>> drivers/devfreq/devfreq.c | 4 +++- >>> 1 file changed, 3 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c >>> index fe2af6a..a225b94 100644 >>> --- a/drivers/devfreq/devfreq.c >>> +++ b/drivers/devfreq/devfreq.c >>> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev, >>> err = device_register(&devfreq->dev); >>> if (err) { >>> mutex_unlock(&devfreq->lock); >>> - goto err_dev; >>> + put_device(&devfreq->dev); >>> + goto err_out; >> why do you change the goto postion? >> err_out is correct to free the memory of devfreq instance. > Sorry. err_dev is correct instead of err_out. If you will see the comment for device_register(drivers/base/core.c) there is mentioned that 'NOTE: _Never_ directly free @dev after calling this function, even if it returned an error! Always use put_device() to give up the reference initialized in this function instead. Here put_device() will decrement the last reference and then free the memory by calling dev->release. Internally put_device() -> kobject_put() -> kobject_cleanup() which is responsible to call 'dev -> release' and also free other kobject resources. We are releasing devfreq in devfreq_dev_release(). So no need to call kfree() again. It'll be redundant. 'err_out' is correct. > >>> } >>> >>> devfreq->trans_table = devm_kzalloc(&devfreq->dev, >>> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev, >>> mutex_unlock(&devfreq_list_lock); >>> >>> device_unregister(&devfreq->dev); >>> + devfreq = NULL; >> It is wrong. If you initialize the devfreq as NULL, >> never free the 'devfreq' instance. No need to release memory after device_unregister(). driver core will take care of this. It will release memory So no need to call free again. >> >>> err_dev: >>> if (devfreq) >>> kfree(devfreq); >>> >> > ~arvind