ntfs3: init run lock for extend inode

After setting the inode mode of $Extend to a regular file, executing the
truncate system call will enter the do_truncate() routine, causing the
run_lock uninitialized error reported by syzbot.

Prior to patch 4e8011ffec, if the inode mode of $Extend was not set to
a regular file, the do_truncate() routine would not be entered.

Add the run_lock initialization when loading $Extend.

syzbot reported:
INFO: trying to register non-static key.
Call Trace:
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 assign_lock_key+0x133/0x150 kernel/locking/lockdep.c:984
 register_lock_class+0x105/0x320 kernel/locking/lockdep.c:1299
 __lock_acquire+0x99/0xd20 kernel/locking/lockdep.c:5112
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590
 ntfs_set_size+0x140/0x200 fs/ntfs3/inode.c:860
 ntfs_extend+0x1d9/0x970 fs/ntfs3/file.c:387
 ntfs_setattr+0x2e8/0xbe0 fs/ntfs3/file.c:808

Fixes: 4e8011ffec ("ntfs3: pretend $Extend records as regular files")
Reported-by: syzbot+bdeb22a4b9a09ab9aa45@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bdeb22a4b9a09ab9aa45
Tested-by: syzbot+bdeb22a4b9a09ab9aa45@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

fs/ntfs3/inode.c

@@ -472,6 +472,7 @@ static struct inode *ntfs_read_mft(struct inode *inode,
 		/* Records in $Extend are not a files or general directories. */
 		inode->i_op = &ntfs_file_inode_operations;
 		mode = S_IFREG;
+		init_rwsem(&ni->file.run_lock);
 	} else {
 		err = -EINVAL;
 		goto out;