locks: prevent side-effects of locks_release_private before file_lock is initialized

When calling fcntl(fd, F_SETLEASE, lck) [with lck=F_WRLCK or F_RDLCK],
the custom signal or owner (if any were previously set using F_SETSIG
or F_SETOWN fcntls) would be reset when F_SETLEASE was called for the
second time on the same file descriptor.

This bug is a regression of 2.6.37 and is described here:
https://bugzilla.kernel.org/show_bug.cgi?id=43336

This patch reverts a commit from Oct 2004 (with subject "nfs4 lease:
move the f_delown processing") which originally introduced the
lm_release_private callback.
Signed-off-by: Filipe Brandenburger <filbranden@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/locks.c

@@ -427,18 +427,8 @@ static void lease_break_callback(struct file_lock *fl)
 	kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
 }
 
-static void lease_release_private_callback(struct file_lock *fl)
-{
-	if (!fl->fl_file)
-		return;
-
-	f_delown(fl->fl_file);
-	fl->fl_file->f_owner.signum = 0;
-}
-
 static const struct lock_manager_operations lease_manager_ops = {
 	.lm_break = lease_break_callback,
-	.lm_release_private = lease_release_private_callback,
 	.lm_change = lease_modify,
 };
 
@@ -1155,8 +1145,13 @@ int lease_modify(struct file_lock **before, int arg)
 		return error;
 	lease_clear_pending(fl, arg);
 	locks_wake_up_blocks(fl);
-	if (arg == F_UNLCK)
+	if (arg == F_UNLCK) {
+		struct file *filp = fl->fl_file;
+
+		f_delown(filp);
+		filp->f_owner.signum = 0;
 		locks_delete_lock(before);
+	}
 	return 0;
 }