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vfio: Remove extra put/gets around vfio_device->group

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The vfio_device->group value has a get obtained during
vfio_add_group_dev() which gets moved from the stack to vfio_device->group
in vfio_group_create_device().

The reference remains until we reach the end of vfio_del_group_dev() when
it is put back.

Thus anything that already has a kref on the vfio_device is guaranteed a
valid group pointer. Remove all the extra reference traffic.

It is tricky to see, but the get at the start of vfio_del_group_dev() is
actually pairing with the put hidden inside vfio_device_put() a few lines
below.

A later patch merges vfio_group_create_device() into vfio_add_group_dev()
which makes the ownership and error flow on the create side easier to
follow.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Message-Id: <1-v3-225de1400dfc+4e074-vfio1_jgg@nvidia.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Jason Gunthorpe 2021-03-30 09:53:05 -06:00 committed by Alex Williamson
parent e49d033bdd
commit e572bfb2b6
1 changed files with 2 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
drivers/vfio/vfio.c
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@ -546,14 +546,12 @@ struct vfio_device *vfio_group_create_device(struct vfio_group *group,
kref_init(&device->kref);
device->dev = dev;
/* Our reference on group is moved to the device */
device->group = group;
device->ops = ops;
device->device_data = device_data;
dev_set_drvdata(dev, device);
/* No need to get group_lock, caller has group reference */
vfio_group_get(group);
mutex_lock(&group->device_lock);
list_add(&device->group_next, &group->device_list);
group->dev_counter++;
@ -585,13 +583,11 @@ void vfio_device_put(struct vfio_device *device)
{
struct vfio_group *group = device->group;
kref_put_mutex(&device->kref, vfio_device_release, &group->device_lock);
vfio_group_put(group);
}
EXPORT_SYMBOL_GPL(vfio_device_put);
static void vfio_device_get(struct vfio_device *device)
{
vfio_group_get(device->group);
kref_get(&device->kref);
}
@ -841,14 +837,6 @@ int vfio_add_group_dev(struct device *dev,
vfio_group_put(group);
return PTR_ERR(device);
}
/*
* Drop all but the vfio_device reference. The vfio_device holds
* a reference to the vfio_group, which holds a reference to the
* iommu_group.
*/
vfio_group_put(group);
return 0;
}
EXPORT_SYMBOL_GPL(vfio_add_group_dev);
@ -928,12 +916,6 @@ void *vfio_del_group_dev(struct device *dev)
unsigned int i = 0;
bool interrupted = false;
/*
* The group exists so long as we have a device reference. Get
* a group reference and use it to scan for the device going away.
*/
vfio_group_get(group);
/*
* When the device is removed from the group, the group suddenly
* becomes non-viable; the device has a driver (until the unbind
@ -1008,6 +990,7 @@ void *vfio_del_group_dev(struct device *dev)
if (list_empty(&group->device_list))
wait_event(group->container_q, !group->container);
/* Matches the get in vfio_group_create_device() */
vfio_group_put(group);
return device_data;