From c16eed2cb64089bf7d958db0fe85352f4ceefb4d Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Wed, 14 May 2014 11:19:35 +0200
Subject: libdiskfs: lock-less reference counting of nodes

* libdiskfs/diskfs.h (struct node): Use refcounts_t for reference counting.
(diskfs_node_refcnt_lock): Remove.
(diskfs_node_norefs,diskfs_drop_node): Change comments accordingly.
* libdiskfs/init-init.c: Adjust accordingly.
* libdiskfs/node-drop.c: Likewise.
* libdiskfs/node-make.c: Likewise.
* libdiskfs/node-nput.c: Likewise.
* libdiskfs/node-nputl.c: Likewise.
* libdiskfs/node-nref.c: Likewise.
* libdiskfs/node-nrefl.c: Likewise.
* libdiskfs/node-nrele.c: Likewise.
* libdiskfs/node-nrelel.c: Likewise.
* ext2fs/inode.c: Likewise.
* fatfs/inode.c: Likewise.
* isofs/inode.c: Likewise.
* tmpfs/node.c: Likewise.
* doc/hurd.texi: Likewise.
---
 fatfs/inode.c | 27 ++++++++-------------------
 1 file changed, 8 insertions(+), 19 deletions(-)

(limited to 'fatfs/inode.c')

diff --git a/fatfs/inode.c b/fatfs/inode.c
index 1d670f53..f228618d 100644
--- a/fatfs/inode.c
+++ b/fatfs/inode.c
@@ -55,7 +55,6 @@
    through the nodehash.  */
 static struct node *nodehash[INOHSZ];
 static size_t nodehash_nr_items;
-/* nodecache_lock must be acquired before diskfs_node_refcnt_lock.  */
 static pthread_rwlock_t nodecache_lock = PTHREAD_RWLOCK_INITIALIZER;
 
 static error_t read_node (struct node *np, vm_address_t buf);
@@ -254,14 +253,8 @@ diskfs_node_norefs (struct node *np)
   if (np->dn->translator)
     free (np->dn->translator);
 
-  /* It is safe to unlock diskfs_node_refcnt_lock here for a while because
-     all references to the node have been deleted.  */
   if (np->dn->dirnode)
-    {
-      pthread_spin_unlock (&diskfs_node_refcnt_lock);
-      diskfs_nrele (np->dn->dirnode);
-      pthread_spin_lock (&diskfs_node_refcnt_lock);
-    }
+    diskfs_nrele (np->dn->dirnode);
 
   assert (!np->dn->pager);
 
@@ -279,14 +272,10 @@ diskfs_try_dropping_softrefs (struct node *np)
     {
       /* Check if someone reacquired a reference through the
 	 nodehash.  */
-      unsigned int references;
-      pthread_spin_lock (&diskfs_node_refcnt_lock);
-      references = np->references;
-      pthread_spin_unlock (&diskfs_node_refcnt_lock);
-
-      /* An additional reference is acquired by libdiskfs across calls
-	 to diskfs_try_dropping_softrefs.  */
-      if (references > 1)
+      struct references result;
+      refcounts_references (&np->refcounts, &result);
+
+      if (result.hard > 0)
 	{
 	  /* A reference was reacquired through a hash table lookup.
 	     It's fine, we didn't touch anything yet. */
@@ -392,7 +381,7 @@ read_node (struct node *np, vm_address_t buf)
   /* Files in fatfs depend on the directory that hold the file.  */
   np->dn->dirnode = dp;
   if (dp)
-    dp->references++;
+    refcounts_ref (&dp->refcounts, NULL);
 
   pthread_rwlock_rdlock (&np->dn->dirent_lock);
 
@@ -627,7 +616,7 @@ diskfs_node_iterate (error_t (*fun)(struct node *))
 	/* We acquire a hard reference for node, but without using
 	   diskfs_nref.	 We do this so that diskfs_new_hardrefs will not
 	   get called.	*/
-	node->references++;
+	refcounts_ref (&node->refcounts, NULL);
       }
 
   pthread_rwlock_unlock (&nodecache_lock);
@@ -838,7 +827,7 @@ diskfs_alloc_node (struct node *dir, mode_t mode, struct node **node)
 
   /* FIXME: We know that readnode couldn't put this in.  */
   np->dn->dirnode = dir;
-  dir->references++;
+  refcounts_ref (&dir->refcounts, NULL);
 
   *node = np;
   return 0;
-- 
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