On Mon, 25 Mar 2019 23:47:30 +0530
Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
> On 3/23/2019 4:50 AM, Parav Pandit wrote:
> > device_register() performs put_device() if device_add() fails.
> > This balances with device_initialize().
> >
> > mdev core performing put_device() when device_register() fails,
> > is an error that puts already released device again.
> > Therefore, don't put the device on error.
> >
>
> device_add() on all errors doesn't call put_device(dev). It releases
> reference to its parent, put_device(parent), but not the device itself,
> put_device(dev).
Sort of, device_initialize() initializes the reference count to 1,
device_add() increments the reference count to 2 via the get_device()
and then drops it back to 1 on all exit paths. The oddity is the
failure path of get_device() itself, but that can only happen if passed
a NULL device, where put_device() is a no-op and not relevant here. So
in all cases device_register() returns with a reference count of 1 and
we need to call put_device() to free the allocated object. The below
change would leak the mdev on error. Thanks,
Alex
> > Fixes: 7b96953bc640 ("vfio: Mediated device Core driver")
> > Signed-off-by: Parav Pandit <parav@xxxxxxxxxxxx>
> > ---
> > drivers/vfio/mdev/mdev_core.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index 0212f0e..3e5880a 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -318,10 +318,8 @@ int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid)
> > dev_set_name(&mdev->dev, "%pUl", uuid.b);
> >
> > ret = device_register(&mdev->dev);
> > - if (ret) {
> > - put_device(&mdev->dev);
> > + if (ret)
> > goto mdev_fail;
> > - }
> >
> > ret = mdev_device_create_ops(kobj, mdev);
> > if (ret)
> >
