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@gmail.com Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure") CC: stable@vger.kernel.org Signed-off-by: Jan Kara jack@suse.cz
Thanks, applied.
- Ted