On Thu, Apr 15, 2021 at 05:54:17PM +0200, Jan Kara wrote:
> Eric has noticed that after pagecache read rework, generic/418 is
> occasionally failing for ext4 when blocksize < pagesize. In fact, the
> pagecache rework just made hard to hit race in ext4 more likely. The
> problem is that since ext4 conversion of direct IO writes to iomap
> framework (commit 378f32bab371), we update inode size after direct IO
> write only after invalidating page cache. Thus if buffered read sneaks
> at unfortunate moment like:
>
> CPU1 - write at offset 1k CPU2 - read from offset 0
> iomap_dio_rw(..., IOMAP_DIO_FORCE_WAIT);
> ext4_readpage();
> ext4_handle_inode_extension()
>
> the read will zero out tail of the page as it still sees smaller inode
> size and thus page cache becomes inconsistent with on-disk contents with
> all the consequences.
>
> Fix the problem by moving inode size update into end_io handler which
> gets called before the page cache is invalidated.
>
> Reported-and-tested-by: Eric Whitney <enwlinux@xxxxxxxxx>
> Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
> CC: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Thanks, applied.
- Ted
