lkml.org 
[lkml]   [2017]   [Apr]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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

\
 
 \ /
  Last update: 2017-04-28 16:41    [W:0.045 / U:0.260 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site