Messages in this thread | | | Date | Fri, 28 Apr 2017 16:40:30 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH 1/2] iommu/s390: Fix IOMMU groups |
| |
On Fri, Apr 28, 2017 at 03:20:17PM +0200, Gerald Schaefer wrote: > On Thu, 27 Apr 2017 23:12:32 +0200 > Joerg Roedel <joro@8bytes.org> wrote:
> > This is the way to free an iommu-group. It was missing before probably > > because it was unclear whether the add_device function allocated a group > > or not. So there was no way to know if it needs to be put again in the > > remove_device function. > > Hmm, for the reference count it should not matter whether a new group was > allocated or an existing group found with iommu_group_get(). Our add_device > callback always gets one reference either from iommu_group_get or _alloc, > and then another one from iommu_group_add_device(), after which the first > reference is put again. So there should always be one reference more after > a successful add_device.
Right, my statement above is wrong. The current code is fine, it gets a reference to the group with iommu_group_get/iommu_group_alloc, attaches the device to the group (which takes a reference to the group of its own), and in the end it drops its local reference.
When the device->group link is broken up in the remove_device function, that reference is also dropped. So everything is fine. The additional iommu_group_put() in my patch is wrong.
Regards,
Joerg
| |