atomic ops in fs

404afe5b · Nickolai Zeldovich · 8d8cc662 · 404afe5b
--- a/fs.c
+++ b/fs.c
@@ -264,9 +264,7 @@ iget(uint dev, uint inum)
 struct inode*
 idup(struct inode *ip)
 {
-  acquire(&icache.lock);
-  ip->ref++;
-  release(&icache.lock);
+  __sync_fetch_and_add(&ip->ref, 1);
  return ip;
 }

@@ -307,8 +305,9 @@ iunlock(struct inode *ip)
 void
 iput(struct inode *ip)
 {
+  if(__sync_sub_and_fetch(&ip->ref, 1) == 0) {
    acquire(&icache.lock);
-  if(ip->ref == 1 && ip->nlink == 0){
+    if (ip->nlink == 0){
      // inode is no longer used: truncate and free inode.
      if(ip->flags & I_BUSY)
 	panic("iput busy");
@@ -326,8 +325,8 @@ iput(struct inode *ip)
      ip->flags &= ~I_BUSY;
      cv_wakeup(&ip->cv);
    }
-  ip->ref--;
    release(&icache.lock);
+  }
 }

 // Common idiom: unlock, then put.