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

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  [RFC] iommu: arm-smmu: correct reference count Peng Fan <van.freenix@gmail.com> - 2015-11-03 14:00 +0100
    Re: [RFC] iommu: arm-smmu: correct reference count Will Deacon <will.deacon@arm.com> - 2015-11-03 14:20 +0100
      Re: [RFC] iommu: arm-smmu: correct reference count Will Deacon <will.deacon@arm.com> - 2015-11-06 13:30 +0100
        Re: [RFC] iommu: arm-smmu: correct reference count Peng Fan <van.freenix@gmail.com> - 2015-11-09 06:50 +0100

#1261466 — [RFC] iommu: arm-smmu: correct reference count

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@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Joerg Roedel <joro@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.

 drivers/iommu/arm-smmu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 48a39df..1cab720 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1344,6 +1344,7 @@ static int arm_smmu_add_platform_device(struct device *dev)
 	struct iommu_group *group;
 	struct arm_smmu_master *master;
 	struct arm_smmu_device *smmu = find_smmu_for_device(dev);
+	int ret;
 
 	if (!smmu)
 		return -ENODEV;
@@ -1358,7 +1359,11 @@ static int arm_smmu_add_platform_device(struct device *dev)
 		return PTR_ERR(group);
 
 	iommu_group_set_iommudata(group, &master->cfg, NULL);
-	return iommu_group_add_device(group, dev);
+
+	ret = iommu_group_add_device(group, dev);
+	iommu_group_put(group);
+
+	return ret;
 }
 
 static int arm_smmu_add_device(struct device *dev)
-- 
1.8.4

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#1261492

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@gmail.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Joerg Roedel <joro@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?

Will
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#1263972

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@gmail.com>
> >> Cc: Will Deacon <will.deacon@arm.com>
> >> Cc: Joerg Roedel <joro@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?

Thanks,

Will
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#1265383

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@gmail.com>
>> >> Cc: Will Deacon <will.deacon@arm.com>
>> >> Cc: Joerg Roedel <joro@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
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