[PATCH 10/14] iommufd: Make destroy_rwsem use a lock class per object type

Jason Gunthorpe
2023-02-25T00:28:11Z

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.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/iommu/iommufd/iommufd_private.h | 1 +
drivers/iommu/iommufd/main.c | 11 ++++++++++-
2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 8921761ff98980..cfcda73942b533 100644
--- 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 8597f2fb88da3a..9cba592d0482e7 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -32,6 +32,7 @@ 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;

@@ -39,7 +40,15 @@ 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);

/*
--
2.39.1