Optimise dir-lookup's second-lock

This should avoid some lock contention.

* libdiskfs/dir-lookup.c (diskfs_S_dir_lookup): Before releasing &np->lock
to get &dnp->lock safely, try to lock &dnp->lock directly.
* libtreefs/dir-lookup.c (_treefs_s_dir_lookup): Likewise.

1 files changed, 6 insertions, 3 deletions

diff --git a/libdiskfs/dir-lookup.c b/libdiskfs/dir-lookup.c
index 1efdf75c..923be033 100644
--- a/libdiskfs/dir-lookup.c
+++ b/libdiskfs/dir-lookup.c
@@ -310,9 +310,12 @@ diskfs_S_dir_lookup (struct protid *dircred,
 		pthread_mutex_lock (&dnp->lock);
 	      else
 		{
-		  pthread_mutex_unlock (&np->lock);
-		  pthread_mutex_lock (&dnp->lock);
-		  pthread_mutex_lock (&np->lock);
+		  if (pthread_mutex_trylock (&dnp->lock))
+		    {
+		      pthread_mutex_unlock (&np->lock);
+		      pthread_mutex_lock (&dnp->lock);
+		      pthread_mutex_lock (&np->lock);
+		    }
 		}
 	    }
 	}