CVE-2021-47327: Improper Update of Reference Count

In the Linux kernel, the following vulnerability has been resolved:

iommu/arm-smmu: Fix arm_smmu_device refcount leak when arm_smmu_rpm_get fails

arm_smmu_rpm_get() invokes pm_runtime_get_sync(), which increases the refcount of the "smmu" even though the return value is less than 0.

The reference counting issue happens in some error handling paths of arm_smmu_rpm_get() in its caller functions. When arm_smmu_rpm_get() fails, the caller functions forget to decrease the refcount of "smmu" increased by arm_smmu_rpm_get(), causing a refcount leak.

Fix this issue by calling pm_runtime_resume_and_get() instead of pm_runtime_get_sync() in arm_smmu_rpm_get(), which can keep the refcount balanced in case of failure.