iommufd: Make destroy_rwsem use a lock class per object type

The selftest invokes things like replace under the object lock of its
idev which protects the idev in a similar way to a real user.
Unfortunately this triggers lockdep. A lock class per type will solve the
problem.

Link: https://lore.kernel.org/r/15-v8-6659224517ea+532-iommufd_alloc_jgg@nvidia.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 47fed9f..9394f0e 100644 (file)
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -119,6 +119,7 @@ enum iommufd_object_type {
 #ifdef CONFIG_IOMMUFD_TEST
        IOMMUFD_OBJ_SELFTEST,
 #endif
+       IOMMUFD_OBJ_MAX,
 };
 
 /* Base struct for all objects with a userspace ID handle. */

diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 521225c..56cdf3c 100644 (file)
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -33,6 +33,7 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
                                             size_t size,
                                             enum iommufd_object_type type)
 {
+       static struct lock_class_key obj_keys[IOMMUFD_OBJ_MAX];
        struct iommufd_object *obj;
        int rc;
 
@@ -40,7 +41,15 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx,
        if (!obj)
                return ERR_PTR(-ENOMEM);
        obj->type = type;
-       init_rwsem(&obj->destroy_rwsem);
+       /*
+        * In most cases the destroy_rwsem is obtained with try so it doesn't
+        * interact with lockdep, however on destroy we have to sleep. This
+        * means if we have to destroy an object while holding a get on another
+        * object it triggers lockdep. Using one locking class per object type
+        * is a simple and reasonable way to avoid this.
+        */
+       __init_rwsem(&obj->destroy_rwsem, "iommufd_object::destroy_rwsem",
+                    &obj_keys[type]);
        refcount_set(&obj->users, 1);
 
        /*