Re: [PATCH v3] ext4: Properly sync file size update after O_SYNC direct IO

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Jan Kara <jack@suse.cz> writes:

> 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>
> ---
>  fs/ext4/file.c | 153 +++++++++++++++++++++----------------------------
>  1 file changed, 65 insertions(+), 88 deletions(-)
>
> Changes since v2:
> * Added more comments explaining the code flow
> * Added WARN_ON_ONCE to verify extending IO is handled synchronously
>
> Changes since v1:
> * Rebased on top of Linus' tree (instead of a tree with iomap cleanup)
> * Made ext4_dio_write_end_io() always return number of written bytes on
>   success for consistency

Thanks for addressing it. It's always better to have a consistent return
value wherever possible.

> * Added Fixes tag

Looks good to me. Please feel free to add - 

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>