CIFS: Protect i_nlink from being negative

that can cause warning messages.  Pavel had initially
suggested a smaller patch around drop_nlink, after
a similar problem was discovered NFS.  Protecting
additional places where nlink is touched was
suggested by Jeff Layton and is included in this.

Reviewed-by: Pavel Shilovsky <pshilovsky@samba.org>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/link.c

@@ -433,7 +433,9 @@ cifs_hardlink(struct dentry *old_file, struct inode *inode,
 	if (old_file->d_inode) {
 		cifsInode = CIFS_I(old_file->d_inode);
 		if (rc == 0) {
+			spin_lock(&old_file->d_inode->i_lock);
 			inc_nlink(old_file->d_inode);
+			spin_unlock(&old_file->d_inode->i_lock);
 /* BB should we make this contingent on superblock flag NOATIME? */
 /*			old_file->d_inode->i_ctime = CURRENT_TIME;*/
 			/* parent dir timestamps will update from srv