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Date:   Mon, 1 Jul 2019 11:24:42 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Kirti Wankhede <kwankhede@nvidia.com>
Cc:     <cohuck@redhat.com>, <kvm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] mdev: Send uevents around parent device registration
Message-ID: <20190701112442.176a8407@x1.home>
In-Reply-To: <08597ab4-cc37-3973-8927-f1bc430f6185@nvidia.com>
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        <08597ab4-cc37-3973-8927-f1bc430f6185@nvidia.com>
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On Mon, 1 Jul 2019 22:43:10 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> On 7/1/2019 8:24 PM, Alex Williamson wrote:
> > This allows udev to trigger rules when a parent device is registered
> > or unregistered from mdev.
> > 
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > ---
> > 
> > v2: Don't remove the dev_info(), Kirti requested they stay and
> >     removing them is only tangential to the goal of this change.
> >   
> 
> Thanks.
> 
> 
> >  drivers/vfio/mdev/mdev_core.c |    8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index ae23151442cb..7fb268136c62 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -146,6 +146,8 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
> >  {
> >  	int ret;
> >  	struct mdev_parent *parent;
> > +	char *env_string = "MDEV_STATE=registered";
> > +	char *envp[] = { env_string, NULL };
> >  
> >  	/* check for mandatory ops */
> >  	if (!ops || !ops->create || !ops->remove || !ops->supported_type_groups)
> > @@ -197,6 +199,8 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
> >  	mutex_unlock(&parent_list_lock);
> >  
> >  	dev_info(dev, "MDEV: Registered\n");
> > +	kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
> > +
> >  	return 0;
> >  
> >  add_dev_err:
> > @@ -220,6 +224,8 @@ EXPORT_SYMBOL(mdev_register_device);
> >  void mdev_unregister_device(struct device *dev)
> >  {
> >  	struct mdev_parent *parent;
> > +	char *env_string = "MDEV_STATE=unregistered";
> > +	char *envp[] = { env_string, NULL };
> >  
> >  	mutex_lock(&parent_list_lock);
> >  	parent = __find_parent_device(dev);
> > @@ -243,6 +249,8 @@ void mdev_unregister_device(struct device *dev)
> >  	up_write(&parent->unreg_sem);
> >  
> >  	mdev_put_parent(parent);
> > +
> > +	kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);  
> 
> mdev_put_parent() calls put_device(dev). If this is the last instance
> holding device, then on put_device(dev) dev would get freed.
> 
> This event should be before mdev_put_parent()

So you're suggesting the vendor driver is calling
mdev_unregister_device() without a reference to the struct device that
it's passing to unregister?  Sounds bogus to me.  We take a
reference to the device so that it can't disappear out from under us,
the caller cannot rely on our reference and the caller provided the
struct device.  Thanks,

Alex