ext4: properly sync file size update after O_SYNC direct IO

ext4: properly sync file size update after O_SYNC direct IO

Gao Xiang has reported that on ext4 O_SYNC direct IO does not properly
sync file size update and thus if we crash at unfortunate moment, the
file can have smaller size although O_SYNC IO has reported successful
completion. The problem happens because update of on-disk inode size is
handled in ext4_dio_write_iter() *after* iomap_dio_rw() (and thus
dio_complete() in particular) has returned and generic_file_sync() gets
called by dio_complete(). Fix the problem by handling on-disk inode size
update directly in our ->end_io completion handler.

References: https://lore.kernel.org/all/02d18236-26ef-09b0-90ad-030c4fe3ee20@linux.alibaba.com
Reported-by: Gao Xiang <hsiangkao@linux.alibaba.com>
CC: stable@vger.kernel.org
Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20231013121350.26872-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>