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

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] fs: ntfs: sleeping in IOCB_NOWAIT path via inode_dio_wait()
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commit 8795f10ca6e1ad5705cf4c0e2062d0271399c2d2
Author: Jiale Yao <yaojiale02@163.com>

ntfs: drain in-flight DIO before buffered write fallback

This commit adds a wait for in-flight direct I/O before falling back
to buffered I/O in the NTFS write path. This prevents data corruption
caused by concurrent direct and buffered I/O dirtying the same pages.

Link: https://lore.kernel.org/r/20260629113827.4074335-3-libaokun@linux.alibaba.com

> diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
> index 8164326b7812a..329871bb476f4 100644
> --- a/fs/ntfs/file.c
> +++ b/fs/ntfs/file.c
> @@ -526,6 +526,13 @@ 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));
> +

[Severity: Medium]
Does this unconditional wait violate the non-blocking semantics of IOCB_NOWAIT?

If an asynchronous direct write with IOCB_NOWAIT is issued, and iomap_dio_rw()
returns -ENOTBLK (for example, if kiocb_invalidate_pages() fails with -EBUSY
due to a concurrently instantiated page), the code enters this buffered I/O
fallback path in ntfs_dio_write_iter().

Calling inode_dio_wait() here will unconditionally sleep if there are other
concurrent direct I/Os in flight on the inode.

Could this stall async I/O worker threads (such as those in io_uring) and
cause unexpected latency spikes when it should instead return -EAGAIN?

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

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Sashiko AI review · https://sashiko.dev/#/patchset/20260924110544.601390-1-yaojiale02@163.com?part=2