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From: Jason Wang <jasowang@redhat.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: "mst@redhat.com" <mst@redhat.com>,
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Subject: Re: [PATCH 4/5] virtio: introduce a vDPA based transport
Date: Mon, 20 Jan 2020 15:52:12 +0800
Message-ID: <bff37791-9640-39e0-5e93-c905ebfb5d2b@redhat.com> (raw)
In-Reply-To: <20200117140013.GV20978@mellanox.com>


On 2020/1/17 下午10:00, Jason Gunthorpe wrote:
> On Fri, Jan 17, 2020 at 05:32:35PM +0800, Jason Wang wrote:
>>>> +	const struct vdpa_config_ops *ops = vdpa->config;
>>>> +	struct virtio_vdpa_device *vd_dev;
>>>> +	int rc;
>>>> +
>>>> +	vd_dev = devm_kzalloc(dev, sizeof(*vd_dev), GFP_KERNEL);
>>>> +	if (!vd_dev)
>>>> +		return -ENOMEM;
>>> This is not right, the struct device lifetime is controled by a kref,
>>> not via devm. If you want to use a devm unwind then the unwind is
>>> put_device, not devm_kfree.
>> I'm not sure I get the point here. The lifetime is bound to underlying vDPA
>> device and devres allow to be freed before the vpda device is released. But
>> I agree using devres of underlying vdpa device looks wired.
> Once device_initialize is called the only way to free a struct device
> is via put_device, while here you have a devm trigger that will
> unconditionally do kfree on a struct device without respecting the
> reference count.
>
> reference counted memory must never be allocated with devm.


Right, fixed.


>
>>>> +	vd_dev->vdev.dev.release = virtio_vdpa_release_dev;
>>>> +	vd_dev->vdev.config = &virtio_vdpa_config_ops;
>>>> +	vd_dev->vdpa = vdpa;
>>>> +	INIT_LIST_HEAD(&vd_dev->virtqueues);
>>>> +	spin_lock_init(&vd_dev->lock);
>>>> +
>>>> +	vd_dev->vdev.id.device = ops->get_device_id(vdpa);
>>>> +	if (vd_dev->vdev.id.device == 0)
>>>> +		return -ENODEV;
>>>> +
>>>> +	vd_dev->vdev.id.vendor = ops->get_vendor_id(vdpa);
>>>> +	rc = register_virtio_device(&vd_dev->vdev);
>>>> +	if (rc)
>>>> +		put_device(dev);
>>> And a ugly unwind like this is why you want to have device_initialize()
>>> exposed to the driver,
>> In this context, which "driver" did you mean here? (Note, virtio-vdpa is the
>> driver for vDPA bus here).
> 'driver' is the thing using the 'core' library calls to implement a
> device, so here the 'vd_dev' is the driver and
> 'register_virtio_device' is the core


Ok.


>
>>> Where is the various THIS_MODULE's I expect to see in a scheme like
>>> this?
>>>
>>> All function pointers must be protected by a held module reference
>>> count, ie the above probe/remove and all the pointers in ops.
>> Will double check, since I don't see this in other virtio transport drivers
>> (PCI or MMIO).
> pci_register_driver is a macro that provides a THIS_MODULE, and the
> pci core code sets driver.owner, then the rest of the stuff related to
> driver ops is supposed to work against that to protect the driver ops.
>
> For the device module refcounting you either need to ensure that
> 'unregister' is a strong fence and guanentees that no device ops are
> called past unregister (noting that this is impossible for release),
> or you need to hold the module lock until release.
>
> It is common to see non-core subsystems get this stuff wrong.
>
> Jason


Ok. I see.

Thanks


  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 12:42 [PATCH 0/5] vDPA support Jason Wang
2020-01-16 12:42 ` [PATCH 1/5] vhost: factor out IOTLB Jason Wang
2020-01-17  4:14   ` Randy Dunlap
2020-01-17  9:34     ` Jason Wang
2020-01-18  0:01   ` kbuild test robot
2020-01-18  0:40   ` kbuild test robot
2020-01-16 12:42 ` [PATCH 2/5] vringh: IOTLB support Jason Wang
2020-01-17 21:54   ` kbuild test robot
2020-01-17 22:33   ` kbuild test robot
2020-01-16 12:42 ` [PATCH 3/5] vDPA: introduce vDPA bus Jason Wang
2020-01-16 15:22   ` Jason Gunthorpe
2020-01-17  3:03     ` Jason Wang
2020-01-17 13:54       ` Jason Gunthorpe
2020-01-20  7:50         ` Jason Wang
2020-01-20 12:17         ` Michael S. Tsirkin
2020-01-20 17:50           ` Jason Gunthorpe
2020-01-20 21:56             ` Michael S. Tsirkin
2020-01-21 14:12               ` Jason Gunthorpe
2020-01-21 14:15                 ` Michael S. Tsirkin
2020-01-21 14:16                   ` Jason Gunthorpe
2020-01-21  8:40       ` Tian, Kevin
2020-01-21  9:41         ` Jason Wang
2020-01-17  4:16   ` Randy Dunlap
2020-01-17  9:34     ` Jason Wang
2020-01-17 12:13   ` Michael S. Tsirkin
2020-01-17 13:52     ` Jason Wang
     [not found]       ` <CAJPjb1+fG9L3=iKbV4Vn13VwaeDZZdcfBPvarogF_Nzhk+FnKg@mail.gmail.com>
2020-01-19  9:07         ` Shahaf Shuler
2020-01-19  9:59           ` Michael S. Tsirkin
2020-01-20  8:44             ` Jason Wang
2020-01-20 12:09               ` Michael S. Tsirkin
2020-01-21  3:32                 ` Jason Wang
2020-01-20  8:43           ` Jason Wang
2020-01-20 17:49             ` Jason Gunthorpe
2020-01-20 20:51               ` Shahaf Shuler
2020-01-20 21:25                 ` Michael S. Tsirkin
2020-01-20 21:47                   ` Shahaf Shuler
2020-01-20 21:59                     ` Michael S. Tsirkin
2020-01-21  6:01                       ` Shahaf Shuler
2020-01-21  7:57                         ` Jason Wang
2020-01-21 14:07                   ` Jason Gunthorpe
2020-01-21 14:16                     ` Michael S. Tsirkin
2020-01-20 21:48               ` Michael S. Tsirkin
2020-01-21  4:00               ` Jason Wang
2020-01-21  5:47                 ` Michael S. Tsirkin
2020-01-21  8:00                   ` Jason Wang
2020-01-21  8:15                     ` Michael S. Tsirkin
2020-01-21  8:35                       ` Jason Wang
2020-01-21 11:09                         ` Shahaf Shuler
2020-01-22  6:36                           ` Jason Wang
2020-01-21 14:05                       ` Jason Gunthorpe
2020-01-21 14:17                         ` Michael S. Tsirkin
2020-01-22  6:18                           ` Jason Wang
2020-01-20  8:19         ` Jason Wang
2020-01-16 12:42 ` [PATCH 4/5] virtio: introduce a vDPA based transport Jason Wang
2020-01-16 15:38   ` Jason Gunthorpe
2020-01-17  9:32     ` Jason Wang
2020-01-17 14:00       ` Jason Gunthorpe
2020-01-20  7:52         ` Jason Wang [this message]
2020-01-17  4:10   ` Randy Dunlap
2020-01-16 12:42 ` [PATCH 5/5] vdpasim: vDPA device simulator Jason Wang
2020-01-16 15:47   ` Jason Gunthorpe
2020-01-17  9:32     ` Jason Wang
2020-01-17 14:10       ` Jason Gunthorpe
2020-01-20  8:01         ` Jason Wang
2020-02-04  4:19         ` Jason Wang
2020-01-17  4:12   ` Randy Dunlap
2020-01-17  9:35     ` Jason Wang
2020-01-18 18:18   ` kbuild test robot
2020-01-28  3:32   ` Dan Carpenter
2020-02-04  4:07     ` Jason Wang
2020-02-04  8:21   ` Zhu Lingshan
2020-02-04  8:28     ` Jason Wang
2020-02-04 12:52       ` Jason Gunthorpe
2020-02-05  3:14         ` Jason Wang
2020-01-21  8:44 ` [PATCH 0/5] vDPA support Tian, Kevin
2020-01-21  9:39   ` Jason Wang

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