Re: [PATCH v4 1/4] uacce: fix for cdev memory leak

[linwenkai (C)]

在 2025/10/22 14:17, Zhangfei Gao 写道:
> On Wed, 22 Oct 2025 at 10:12, Chenghai Huang <huangchenghai2@xxxxxxxxxx> wrote:
> > From: Wenkai Lin <linwenkai6@xxxxxxxxxxxxx>
> >
> > In uacce_register(), if cdev_device_add() fails, we should properly
> > decrease the reference count of the cdev kobject and set uacce->cdev
> > to NULL to avoid potential use-after-free or double free issues.
> >
> > This change adds proper error handling after cdev_device_add() fails,
> > ensuring that kobject_put() is called and uacce->cdev is cleared.
> >
> > Fixes: 015d239ac014 ("uacce: add uacce driver")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Wenkai Lin <linwenkai6@xxxxxxxxxxxxx>
> > Signed-off-by: Chenghai Huang <huangchenghai2@xxxxxxxxxx>
> > ---
> >   drivers/misc/uacce/uacce.c | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/misc/uacce/uacce.c b/drivers/misc/uacce/uacce.c
> > index 42e7d2a2a90c..9b82a6731832 100644
> > --- a/drivers/misc/uacce/uacce.c
> > +++ b/drivers/misc/uacce/uacce.c
> > @@ -519,6 +519,8 @@ EXPORT_SYMBOL_GPL(uacce_alloc);
> >    */
> >   int uacce_register(struct uacce_device *uacce)
> >   {
> > +       int ret;
> > +
> >          if (!uacce)
> >                  return -ENODEV;
> >
> > @@ -529,7 +531,14 @@ int uacce_register(struct uacce_device *uacce)
> >          uacce->cdev->ops = &uacce_fops;
> >          uacce->cdev->owner = THIS_MODULE;
> >
> > -       return cdev_device_add(uacce->cdev, &uacce->dev);
> > +       ret = cdev_device_add(uacce->cdev, &uacce->dev);
> > +       if (ret) {
> > +               kobject_put(&uacce->cdev->kobj);
> Not understanding this,
> What if kobject_put(&p->kobj) is called twice?
> cdev_device_add would call cdev_del->kobject_put(&p->kobj) as well.
>
> If you think cdev_device_add has an issue, maybe fixing
> cdev_device_add itself is better?
>
> Thanks
After more testing, a new conclusion was reached.

After the cdev_set_parent function in cdev_device_add is called,
the cdev and the device will share the same lifetime and the memory
of the cdev is managed by the device.
So when put_device is called in the uacce_remove, the memory of the cdev
will also be released, so there is no memory leak issue in the code.

In addition, when cdev_device_add fails, a flag should be set to detect
this situation to prevent the uacce_remove from incorrectly calling
cdev_device_del to release the unallocated resources.
This issue will be fixed in the next patch.

Thanks,
Wenkai