RDMA/mlx5: Use RCU and direct refcounts to keep memory alive

dispatch_event_fd() runs from a notifier with minimal locking, and relies
on RCU and a file refcount to keep the uobject and eventfd alive.

As the next patch wants to remove the file_operations release function
from the drivers, re-organize things so that the devx_event_notifier()
path uses the existing RCU to manage the lifetime of the uobject and
eventfd.

Move the refcount puts to a call_rcu so that the objects are guaranteed to
exist and remove the indirect file refcount.

Link: https://lore.kernel.org/r/1578504126-9400-2-git-send-email-yishaih@mellanox.com
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/rdma/uverbs_types.h b/include/rdma/uverbs_types.h
index 0b0f5a5f392d..ca65d4704b4b 100644
--- a/include/rdma/uverbs_types.h
+++ b/include/rdma/uverbs_types.h
@@ -144,6 +144,18 @@ void rdma_alloc_abort_uobject(struct ib_uobject *uobj,
 int __must_check rdma_alloc_commit_uobject(struct ib_uobject *uobj,
 					   struct uverbs_attr_bundle *attrs);
 
+/*
+ * uverbs_uobject_get is called in order to increase the reference count on
+ * an uobject. This is useful when a handler wants to keep the uobject's memory
+ * alive, regardless if this uobject is still alive in the context's objects
+ * repository. Objects are put via uverbs_uobject_put.
+ */
+static inline void uverbs_uobject_get(struct ib_uobject *uobject)
+{
+	kref_get(&uobject->ref);
+}
+void uverbs_uobject_put(struct ib_uobject *uobject);
+
 struct uverbs_obj_fd_type {
 	/*
 	 * In fd based objects, uverbs_obj_type_ops points to generic