Re: [PATCH 08/12] ext4: hold i_rwsem until AIO completes

Theodore Y. Ts'o
2020-01-14T21:51:04Z

On Tue, Jan 14, 2020 at 05:12:21PM +0100, Christoph Hellwig wrote:
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 0e8708b77da6..b6aa2d249b30 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4777,9 +4777,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
> if (mode & FALLOC_FL_KEEP_SIZE)
> flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
>
> - /* Wait all existing dio workers, newcomers will block on i_mutex */
> - inode_dio_wait(inode);
> -
> /* Preallocate the range including the unaligned edges */
> if (partial_begin || partial_end) {
> ret = ext4_alloc_file_blocks(file,

I note that you've dropped the inode_dio_wait() in ext4's ZERO_RANGE,
COLLAPSE_RANGE, INSERT_RANGE, etc. We had added these to avoid
problems when various fallocate operations which modify the inode's
logical->physical block mapping racing with direct I/O (both reads or
writes).

I don't see a replacement protection in this patch series. How does
are file systems supported to protect against such races?

- Ted