Re: [PATCH 2/3] ntfs: drain in-flight DIO before buffered write fallback

[liubaolin]

在 2026/9/24 19:05, Jiale Yao 写道:
> 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, iomap_file_buffered_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.  NTFS 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 iomap_file_buffered_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: 9c87959601e8 ("ntfs: update file operations")
> Link: https://lore.kernel.org/r/20260629113827.4074335-3-libaokun@xxxxxxxxxxxxxxxxx
> Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>
> ---
>   fs/ntfs/file.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
> index 007d1614b9ac..2fc2ffde3846 100644
> --- a/fs/ntfs/file.c
> +++ b/fs/ntfs/file.c
> @@ -527,6 +527,13 @@ static ssize_t ntfs_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   
>   		offset = iocb->ki_pos;
>   		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(file_inode(iocb->ki_filp));

Hi Jiale,
   This fallback path can still have IOCB_NOWAIT set, but 
inode_dio_wait() blocks when there is outstanding DIO. Clearing 
IOCB_DIRECT does not clear IOCB_NOWAIT.

  In comparison, ext4_buffered_write_iter() rejects NOWAIT requests 
before reaching the wait.

  Could we also handle IOCB_NOWAIT before entering this potentially 
blocking fallback?
  If no bytes have been written, we can return -EAGAIN; if some DIO has 
already completed, we should preserve the positive short-write result.

Thanks,
Baolin.


> +
>   		written = iomap_file_buffered_write(iocb, from,
>   				&ntfs_write_iomap_ops, &ntfs_iomap_folio_ops,
>   				NULL);