From e572bfb2b6a83b05acd30c03010e661b1967960f Mon Sep 17 00:00:00 2001 From: Jason Gunthorpe Date: Tue, 30 Mar 2021 09:53:05 -0600 Subject: [PATCH] vfio: Remove extra put/gets around vfio_device->group 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 Reviewed-by: Kevin Tian Reviewed-by: Max Gurtovoy Reviewed-by: Cornelia Huck Reviewed-by: Eric Auger Signed-off-by: Jason Gunthorpe Message-Id: <1-v3-225de1400dfc+4e074-vfio1_jgg@nvidia.com> Signed-off-by: Alex Williamson --- drivers/vfio/vfio.c | 21 ++------------------- 1 file changed, 2 insertions(+), 19 deletions(-) diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c index 38779e6fd80c..15d8e678e556 100644 --- a/drivers/vfio/vfio.c +++ b/drivers/vfio/vfio.c @@ -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; -- 2.20.1