KEYS: Define a __key_get() wrapper to use rather than atomic_inc()

Define a __key_get() wrapper to use rather than atomic_inc() on the key usage
count as this makes it easier to hook in refcount error debugging.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index b42f2d4..87eff32 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -479,7 +479,7 @@
 
 	/* we found a viable match */
 found:
-	atomic_inc(&key->usage);
+	__key_get(key);
 	key->last_used_at = ctx->now.tv_sec;
 	keyring->last_used_at = ctx->now.tv_sec;
 	while (sp > 0)
@@ -573,7 +573,7 @@
 	return ERR_PTR(-ENOKEY);
 
 found:
-	atomic_inc(&key->usage);
+	__key_get(key);
 	keyring->last_used_at = key->last_used_at =
 		current_kernel_time().tv_sec;
 	rcu_read_unlock();
@@ -909,7 +909,7 @@
 
 	klist = rcu_dereference_locked_keyring(keyring);
 
-	atomic_inc(&key->usage);
+	__key_get(key);
 	keyring->last_used_at = key->last_used_at =
 		current_kernel_time().tv_sec;