Re: [PATCH v2] chardev: fix error handling in cdev_device_add()

[Yang Yingliang]

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@xxxxxxxxxx>
> > ---
> > v1 -> v2:
> >    Add information to update commit message.
> >    v1 link: https://lore.kernel.org/lkml/1959fa74-b06c-b8bc-d14f-b71e5c4290ee@xxxxxxxxxx/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
> .