linux-kernel - Re: [PATCH v2] chardev: fix error handling in cdev_device

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Date:   Tue, 25 Oct 2022 21:20:12 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <logang@...tatee.com>, <dan.j.williams@...el.com>,
        <hans.verkuil@...co.com>, <alexandre.belloni@...e-electrons.com>,
        <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2] chardev: fix error handling in cdev_device_add()

Hi, Greg

On 2022/10/25 19:50, Greg KH wrote:
> On Tue, Oct 25, 2022 at 07:39:57PM +0800, Yang Yingliang wrote:
>> While doing fault injection test, I got the following report:
>>
>> ------------[ cut here ]------------
>> kobject: '(null)' (0000000039956980): is not initialized, yet kobject_put() is being called.
>> WARNING: CPU: 3 PID: 6306 at kobject_put+0x23d/0x4e0
>> CPU: 3 PID: 6306 Comm: 283 Tainted: G        W          6.1.0-rc2-00005-g307c1086d7c9 #1253
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>> RIP: 0010:kobject_put+0x23d/0x4e0
>> Call Trace:
>>   <TASK>
>>   cdev_device_add+0x15e/0x1b0
>>   __iio_device_register+0x13b4/0x1af0 [industrialio]
>>   __devm_iio_device_register+0x22/0x90 [industrialio]
>>   max517_probe+0x3d8/0x6b4 [max517]
>>   i2c_device_probe+0xa81/0xc00
>>
>> When device_add() is injected fault and returns error, if dev->devt is not set,
>> cdev_add() is not called, cdev_del() is not needed. Fix this by checking dev->devt
>> in error path.
> Nit, please wrap your changelog text at 72 columns.
>
>> Fixes: 233ed09d7fda ("chardev: add helper function to register char devs with a struct device")
>> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
>> ---
>> v1 -> v2:
>>    Add information to update commit message.
>>    v1 link: https://lore.kernel.org/lkml/1959fa74-b06c-b8bc-d14f-b71e5c4290ee@huawei.com/T/
>> ---
>>   fs/char_dev.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/char_dev.c b/fs/char_dev.c
>> index ba0ded7842a7..3f667292608c 100644
>> --- a/fs/char_dev.c
>> +++ b/fs/char_dev.c
>> @@ -547,7 +547,7 @@ int cdev_device_add(struct cdev *cdev, struct device *dev)
>>   	}
>>   
>>   	rc = device_add(dev);
>> -	if (rc)
>> +	if (rc && dev->devt)
> No, this is a layering violation and one that you do not know is really
> going to be true or not.  the devt being present, or not, should not be
> an issue of if the device_add failed or not.  This isn't correct, sorry.
Do you mean it's not a bug or the warn can be ignored or it's bug in 
driver ?
I see devt is checked before calling cdev_del() in cdev_device_del().

Thanks,
Yang
>
> thanks,
>
> greg k-h
> .