[RFC] iommu: arm-smmu: correct reference count

[Peng Fan]

Hi Will,

On Fri, Nov 06, 2015 at 12:23:39PM +0000, Will Deacon wrote:
>On Wed, Nov 04, 2015 at 10:48:28AM +0800, Peng Fan wrote:
>> On Tue, Nov 03, 2015 at 01:17:34PM +0000, Will Deacon wrote:
>> >On Tue, Nov 03, 2015 at 08:59:17PM +0800, Peng Fan wrote:
>> >> iommu_group_alloc will initialize the reference count for group to 1.
>> >> iommu_group_add_device also increase the group reference count,
>> >> if nothing bad happends. And we need to add iommu_group_put to
>> >> decrease the reference count for group.
>> >> 
>> >> Signed-off-by: Peng Fan <van.freenix at gmail.com>
>> >> Cc: Will Deacon <will.deacon at arm.com>
>> >> Cc: Joerg Roedel <joro at 8bytes.org>
>> >> ---
>> >> 
>> >> Not sure whether my understanding is correct or not. I checked rockchip-iommu.c
>> >> exynos-iommu.c and fsl_pamu_domain.c, and they all have iommu_group_put after
>> >> iommu_group_add_device.
>> >
>> >Doesn't this pair up with the iommu_group_remove_device in
>> >arm_smmu_remove_device? Are you actually seeing an issue in practice?
>> 
>> In arm_smmu_add_platform_device,
>> iommu_group_alloc --> group->device_kobj ref count will be init to 1.
>> iommu_group_add_device --> group->device_kobj ref count will be added 1 to 2.
>> 
>> In arm_smmu_remove_device:
>> iommu_group_remove_device --> Decrease group->device_kobj ref count by 1.
>> After arm_smmu_remove_device, the ref count of group->device_kobj is not 0.
>> 
>> So I think need to add iommu_group_put after iommu_group_add_device.
>> If I am wrong, please correct me.
>
>Ok, I see what you're saying. iommu_group_get_for_dev has exactly the
>same issue, so could you update arm-smmu-v3.c as well, please?

I did not see the update about device_group for iommu, when I worked out this patch.
Rebased to latest linux/master, whether to arm-smmu.c or arm-smmu-v3.c,
only add 'iommu_group_put' at the end of iommu_group_get_for_dev is ok as the
following.

I'll send out V2.

Thanks,
Peng.

>
>Thanks,
>
>Will