libdiskfs: lock-less reference counting for peropen objects

* libdiskfs/diskfs.h (struct peropen): Use refcount_t for field refcnt.
* libdiskfs/peropen-make.c (diskfs_make_peropen): Initialize refcnt.
* libdiskfs/peropen-rele.c (diskfs_release_peropen): Adjust accordingly.
* libdiskfs/protid-make.c (diskfs_start_protid): Likewise.  Also, the
node must no longer be locked, adjust comment accordingly.
(diskfs_create_protid): Likewise.

1 files changed, 10 insertions, 11 deletions

diff --git a/libdiskfs/peropen-rele.c b/libdiskfs/peropen-rele.c
index d3f74921..877137bb 100644
--- a/libdiskfs/peropen-rele.c
+++ b/libdiskfs/peropen-rele.c
@@ -22,13 +22,8 @@
 void
 diskfs_release_peropen (struct peropen *po)
 {
-  pthread_mutex_lock (&po->np->lock);
-
-  if (--po->refcnt)
-    {
-      pthread_mutex_unlock (&po->np->lock);
-      return;
-    }
+  if (refcount_deref (&po->refcnt) > 0)
+    return;
 
   if (po->root_parent)
     mach_port_deallocate (mach_task_self (), po->root_parent);
@@ -40,10 +35,14 @@ diskfs_release_peropen (struct peropen *po)
     mach_port_deallocate (mach_task_self (), po->shadow_root_parent);
 
   if (po->lock_status != LOCK_UN)
-    fshelp_acquire_lock (&po->np->userlock, &po->lock_status,
-			 &po->np->lock, LOCK_UN);
-
-  diskfs_nput (po->np);
+    {
+      pthread_mutex_lock (&po->np->lock);
+      fshelp_acquire_lock (&po->np->userlock, &po->lock_status,
+                           &po->np->lock, LOCK_UN);
+      diskfs_nput (po->np);
+    }
+  else
+    diskfs_nrele (po->np);
 
   free (po->path);
   free (po);