ext4: block direct I/O writes during ext4_truncate

ext4: block direct I/O writes during ext4_truncate

Just as in ext4_punch_hole() it is important that we block DIO writes
while the truncate is proceeding, since during the overwriting DIO
write, we drop i_mutex, which means a truncate could start while the
Direct I/O operation is still in progress.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org