[PATCH] vfio/iommu_type1: acquire iommu lock in vfio_iommu_type1_release()

[Sidhartha Kumar <sidhartha.kumar@oracle.com>]

From vfio_iommu_type1_release() there is a code path:

vfio_iommu_unmap_unpin_all()
 vfio_remove_dma()
    vfio_unmap_unpin()
      unmap_unpin_slow()
        vfio_unpin_pages_remote()
          vfio_find_vpfn()

This path is taken without acquiring the iommu lock so it could lead to
a race condition in the traversal of the pfn_list rb tree. The lack of
the iommu lock in vfio_iommu_type1_release() was confirmed by adding a

WARN_ON(!mutex_is_locked(&iommu->lock))

which was reported in dmesg. Fix this potential race by adding a iommu
lock and release in vfio_iommu_type1_release().

Suggested-by: Khalid Aziz <khalid.aziz@oracle.com>
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
---
 drivers/vfio/vfio_iommu_type1.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 306e6f1d1c70e..7d2fea1b483dc 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2601,7 +2601,9 @@ static void vfio_iommu_type1_release(void *iommu_data)
 		kfree(group);
 	}
 
+	mutex_lock(&iommu->lock);
 	vfio_iommu_unmap_unpin_all(iommu);
+	mutex_unlock(&iommu->lock);
 
 	list_for_each_entry_safe(domain, domain_tmp,
 				 &iommu->domain_list, next) {
-- 
2.40.1