linux-kernel - Re: [PATCH V1 1/3] rpmsg: glink: Free device context only when cdev not in use

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Message-ID: <613d6852-f307-40f5-ccf0-7a73f1df8fb4@quicinc.com>
Date:   Mon, 14 Feb 2022 20:32:33 +0530
From:   Deepak Kumar Singh <quic_deesin@...cinc.com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
CC:     <bjorn.andersson@...aro.org>, <swboyd@...omium.org>,
        <quic_clew@...cinc.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>,
        <linux-remoteproc@...r.kernel.org>,
        "Ohad Ben-Cohen" <ohad@...ery.com>
Subject: Re: [PATCH V1 1/3] rpmsg: glink: Free device context only when cdev
 not in use


On 2/3/2022 11:05 PM, Mathieu Poirier wrote:
> Hi Deepak,
>
> On Thu, Jan 27, 2022 at 12:34:44AM +0530, Deepak Kumar Singh wrote:
>> Struct device holding cdev should not be freed unless cdev
>> is not in use. It is possible that user space has opened
>> char device while kernel has freed the associated struct
>> device context.
>>
>> Mark dev kobj as parent of cdev, so that chardev_add gets
>> an extra reference to dev. This ensures device context is not
>> freed until cdev is is not in uses.
>> ---
>>   drivers/rpmsg/rpmsg_char.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
>> index c03a118..72ee101 100644
>> --- a/drivers/rpmsg/rpmsg_char.c
>> +++ b/drivers/rpmsg/rpmsg_char.c
>> @@ -417,6 +417,7 @@ static int rpmsg_eptdev_create(struct rpmsg_ctrldev *ctrldev,
>>   	dev->id = ret;
>>   	dev_set_name(dev, "rpmsg%d", ret);
>>   
>> +	cdev_set_parent(&eptdev->cdev, &dev->kobj);
>>   	ret = cdev_add(&eptdev->cdev, dev->devt, 1);
> This issue should have been fixed when cdev_add() was replaced by
> cdev_device_add(), something you will find on v5.17-rc2.
>
> Also, this set is generating checkpatch warnings and as such I will not review
> the other patches in it.
>
> Thanks,
> Mathieu

Thank you Mathieu for info!! i will recheck other 2 patches for 
checkpatch warnings.

Thanks,

Deepak

>>   	if (ret)
>>   		goto free_ept_ida;
>> @@ -533,6 +534,7 @@ static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
>>   	dev->id = ret;
>>   	dev_set_name(&ctrldev->dev, "rpmsg_ctrl%d", ret);
>>   
>> +	cdev_set_parent(&ctrldev->cdev, &dev->kobj);
>>   	ret = cdev_add(&ctrldev->cdev, dev->devt, 1);
>>   	if (ret)
>>   		goto free_ctrl_ida;
>> -- 
>> 2.7.4
>>