Re: [PATCH v3 3/3] exfat: drain in-flight DIO before buffered writes

[Chi Zhiling <chizhiling@163.com>]

On 9/28/26 4:54 PM, Jiale Yao wrote:
> An asynchronous direct write can remain in flight after the inode lock is
> released.  If a buffered write dirties page cache while the direct write
> is still pending, the direct write's post-I/O invalidation can find the
> dirty pages, report a page cache invalidation failure, and record -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.  ExFAT does not drain in-flight DIO before either a regular buffered
> write or the buffered fallback after iomap_dio_rw() returns -ENOTBLK or a
> short write.
> 
> Wait for in-flight DIO before calling iomap_file_buffered_write() in both
> paths.
> 
> 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: 867b9c96dc83 ("exfat: add iomap direct I/O support")
> Link: https://lore.kernel.org/r/20260629113827.4074335-3-libaokun@linux.alibaba.com
> Signed-off-by: Jiale Yao <yaojiale02@163.com>
> ---
>   fs/exfat/file.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/exfat/file.c b/fs/exfat/file.c
> index a2a9ee1a2004..28811210663f 100644
> --- a/fs/exfat/file.c
> +++ b/fs/exfat/file.c
> @@ -807,6 +807,8 @@ static ssize_t exfat_fallback_buffered_write(struct kiocb *iocb,
>   
>   	iocb->ki_flags &= ~IOCB_DIRECT;
>   
> +	inode_dio_wait(file_inode(iocb->ki_filp));
> +
>   	written = iomap_file_buffered_write(iocb, from, &exfat_write_iomap_ops,
>   			NULL, NULL);
>   	if (written < 0)
> @@ -889,11 +891,17 @@ static ssize_t exfat_file_write_iter(struct kiocb *iocb, struct iov_iter *iter)
>   			goto unlock;
>   	}
>   
> -	if (iocb->ki_flags & IOCB_DIRECT)
> +	if (iocb->ki_flags & IOCB_DIRECT) {
>   		ret = exfat_dio_write_iter(iocb, iter);
> -	else
> +	} else {
> +		/*
> +		 * 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);
>   		ret = iomap_file_buffered_write(iocb, iter,
>   				&exfat_write_iomap_ops, NULL, NULL);
> +	}
>   	if (ret < 0)
>   		goto unlock;
>   

Also, if you don't mind, could you add inode_dio_wait() to 
exfat_extend_valid_size() as well?

Thanks.