Re: [PATCH 1/3] ext2: drain in-flight DIO before buffered write fallback

[Jan Kara]

On Thu 24-09-26 18:51:23, Jiale Yao wrote:
> An asynchronous direct write can remain in flight after the inode lock is
> released.  If another direct write falls back to buffered I/O while the
> first write is still pending, generic_perform_write() can dirty pages
> before the first write completes its post-I/O page cache invalidation.
> The invalidation then finds dirty pages, reports a page cache invalidation
> failure, and records -EIO in the mapping error sequence.  A later fsync()
> therefore returns -EIO.
> 
> Commit 15cdefd0c0522f9d5e12d947fa04f4c11649b699 ("ext4: drain
> in-flight DIO before buffered write fallback") fixed the same race in
> ext4.  Ext2 has an equivalent fallback after iomap_dio_rw() returns
> -ENOTBLK or a short write, but does not drain other in-flight DIO before
> dirtying the page cache.
> 
> Wait for in-flight DIO before calling generic_perform_write() in the
> fallback path.
> 
> A reproducer using concurrent AIO direct writes and buffered fallback
> triggered the following warning and made a subsequent fsync() return
> -EIO:
> 
>   Page cache invalidation failure on direct I/O.  Possible data corruption
>   due to collision with buffered I/O!
> 
> Fixes: fb5de4358e1a ("ext2: Move direct-io to use iomap")
> Link: https://lore.kernel.org/r/20260629113827.4074335-3-libaokun@xxxxxxxxxxxxxxxxx
> Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>

Thanks! Added to my tree.

								Honza

> ---
>  fs/ext2/file.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index b9020df7d89e..67fe423c3828 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -135,6 +135,13 @@ static ssize_t ext2_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  		int ret2;
>  
>  		iocb->ki_flags &= ~IOCB_DIRECT;
> +
> +		/*
> +		 * Prevent concurrent direct I/O and buffered I/O to the same file
> +		 * range. Wait for in-flight DIO to finish before dirtying pages.
> +		 */
> +		inode_dio_wait(inode);
> +
>  		pos = iocb->ki_pos;
>  		status = generic_perform_write(iocb, from);
>  		if (unlikely(status < 0)) {
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR