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Subject: Re: [PATCH v2] chardev: fix error handling in cdev_device_add()
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
        <logang@deltatee.com>, <dan.j.williams@intel.com>,
        <hans.verkuil@cisco.com>, <alexandre.belloni@free-electrons.com>,
        <viro@zeniv.linux.org.uk>
References: <20221025113957.693723-1-yangyingliang@huawei.com>
 <Y1fNnwLlY079xGVY@kroah.com>
 <ae7cbce0-3506-e21b-fa9b-37a13fe00b77@huawei.com>
 <Y1fmgCS7fuf/LQBc@kroah.com>
 <65b29177-6892-7578-b2ae-a09d5adab661@huawei.com>
 <Y4id1sc4J9mctEU2@kroah.com>
From:   Yang Yingliang <yangyingliang@huawei.com>
Message-ID: <83280689-206f-668d-665c-0a2a3b8d8838@huawei.com>
Date:   Fri, 2 Dec 2022 09:46:43 +0800
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On 2022/12/1 20:28, Greg KH wrote:
> On Thu, Dec 01, 2022 at 08:06:44PM +0800, Yang Yingliang wrote:
>> Hi Greg,
>>
>> On 2022/10/25 21:37, Greg KH wrote:
>>> On Tue, Oct 25, 2022 at 09:20:12PM +0800, Yang Yingliang wrote:
>>>> 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@huawei.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().
>>> Ah!  The core doesn't set devt, the caller has that set.  That makes
>>> more sense now, sorry for the confusion on my side.
>>>
>>> Yes, this looks correct, the diff didn't have the full context and I was
>>> confused.
>>>
>>> I'll go queue this up, very nice work.
>>>
>>> greg k-h
>> I didn't find this patch in your trees, does it been merged?
> Hm, is this:
> 4634c973096a ("chardev: Fix potential memory leak when cdev_add() failed")
> or is this a different patch?  If different, it's not in my review queue
> anymore, sorry, can you resend it?
It's a different patch, I can resend it.

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