fs: improve DCACHE_REFERENCED usage

dentry referenced bit is only set when installing the dentry back
onto the LRU. However with lazy LRU, the dentry can already be on
the LRU list at dput time, thus missing out on setting the referenced
bit. Fix this.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -246,13 +246,16 @@ void dput(struct dentry *dentry)
 		if (dentry->d_op->d_delete(dentry))
 			goto unhash_it;
 	}
+
 	/* Unreachable? Get rid of it */
  	if (d_unhashed(dentry))
 		goto kill_it;
-  	if (list_empty(&dentry->d_lru)) {
-  		dentry->d_flags |= DCACHE_REFERENCED;
+
+	/* Otherwise leave it cached and ensure it's on the LRU */
+	dentry->d_flags |= DCACHE_REFERENCED;
+	if (list_empty(&dentry->d_lru))
 		dentry_lru_add(dentry);
-  	}
+
  	spin_unlock(&dentry->d_lock);
 	spin_unlock(&dcache_lock);
 	return;