Hi Will,
On Mon, Nov 09, 2015 at 10:10:59AM +0000, Will Deacon wrote:
>On Mon, Nov 09, 2015 at 02:13:28PM +0800, Peng Fan wrote:
>> The basic flow for iommu_group_for_dev is:
>> iommu_group_get_for_dev
>> |-> iommu_group_get : increase reference count by 1.
>> return group;
>> |-> ops->device_group : Init/increase reference count to/by 1.
>> iommu_group_add_device : Increase reference count by 1.
>> return group;
>>
>> We can see that ops->device_group and iommu_group_add_device will together
>> increase the iommu group reference count by 2. Actually we only need 1,
>> but not 2. So we need add iommu_group_put after iommu_group_add_device
>> to make sure iommu_group_get_for_dev only increase reference count by 1.
>>
>> Signed-off-by: Peng Fan <van.free...@gmail.com>
>> Cc: Joerg Roedel <j...@8bytes.org>
>> Cc: Will Deacon <will.dea...@arm.com>
>> ---
>>
>> V1 thread: https://lkml.org/lkml/2015/11/3/304
>> Changes V2:
>> I did not see the update about device_group when I worked out V1. So
>> redo the patch and refine commit msg and rebased to latest linus'
>> linux master tree.
>>
>> drivers/iommu/iommu.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index abae363..9c1971b 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -852,10 +852,10 @@ struct iommu_group *iommu_group_get_for_dev(struct
>> device *dev)
>> }
>>
>> ret = iommu_group_add_device(group, dev);
>> - if (ret) {
>> - iommu_group_put(group);
>> + iommu_group_put(group);
>> +
>> + if (ret)
>> return ERR_PTR(ret);
>> - }
>
>Hmm, I don't think this is correct either:
>
> (1) It doesn't help the arm-smmu driver (which deals with platform
> devices too)
>
> (2) It breaks IOMMU drivers that currently have the explicit put already
> (e.g. amd-iommu.c:init_iommu_group)
>
>The easiest way for you to proceed is to extend your original patch so
>that it also adds an iommu_group_put to the arm-smmu-v3 driver after
>a successful iommu_group_get_for_dev.
I am not sure if the following patch is what you preferred. But this means
that iommu_grou_get_for_dev will increase the group reference count by 2, when
need to create a new group?
diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 4e5118a..9c88301 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1855,6 +1855,9 @@ static int arm_smmu_add_device(struct device *dev)
/* Add the new SID */
sids[smmu_group->num_sids - 1] = sid;
smmu_group->sids = sids;
+
+ iommu_group_put(group);
+
return 0;
out_put_group:
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 47dc7a7..af6afce 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1357,6 +1357,8 @@ static int arm_smmu_add_device(struct device *dev)
if (IS_ERR(group))
return PTR_ERR(group);
+ iommu_group_put(group);
+
return 0;
}
Thanks,
Peng.
>
>Will
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