Re: [PATCH v6 14/31] ext4: implement buffered write path using iomap

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Spurious ENOSPC failures occur on large writes because space exhaustion protection is evaluated only once per write syscall.
--

commit 0e8cfe3183ec36e2c7cb68a2f835e58a2e54d43e
Author: Zhang Yi <yi.zhang@huawei.com>
ext4: implement buffered write path using iomap

This commit introduces new iomap_ops instances for ext4 buffered writes to 
transition to the iomap infrastructure. It also adds ext4_iomap_valid to 
verify extent validity and handles cleanup of stale delayed allocation 
ranges on short writes.

> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 374b4bc25bd5d..50d3c92709c8b 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
[ ... ]
> @@ -330,6 +330,21 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
>  	return count;
>  }
>  
> +static ssize_t ext4_iomap_buffered_write(struct kiocb *iocb,
> +					 struct iov_iter *from)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	const struct iomap_ops *iomap_ops;
> +
> +	if (test_opt(inode->i_sb, DELALLOC) && !ext4_nonda_switch(inode->i_sb))
> +		iomap_ops = &ext4_iomap_buffered_da_write_ops;
> +	else
> +		iomap_ops = &ext4_iomap_buffered_write_ops;
> +

[Severity: High]
Will this cause spurious -ENOSPC failures on multi-gigabyte writes?

In ext4_iomap_buffered_write(), the ext4_nonda_switch() check is evaluated
only once before passing iomap_ops into the iomap_file_buffered_write() loop.

If space runs low during a large write, the operation stays locked in delayed
allocation mode instead of dynamically switching to non-delayed allocation.

This bypasses the continuous per-page free space threshold checks that were
previously done on-the-fly, which could lead to over-reserving space and
silent data loss during background writeback.

> +	return iomap_file_buffered_write(iocb, from, iomap_ops,
> +					 &ext4_iomap_write_ops, NULL);
> +}
> +
>  static ssize_t ext4_buffered_write_iter(struct kiocb *iocb,
>  					struct iov_iter *from)
>  {

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260903123543.2302999-1-yi.zhang@huaweicloud.com?part=14