Re: [syzbot] [ext4?] possible deadlock in ext4_destroy_inline_data (2)

Darrick J. Wong
2025-12-01T23:25:53Z

On Mon, Dec 01, 2025 at 04:17:02PM -0700, Andreas Dilger wrote:
> On Dec 1, 2025, at 9:16 AM, Theodore Tso <tytso@mit.edu> wrote:
> >
> > That being said, we probably should just not try to expand the inode's
> > extra size while evicting the inode. In practice we don't actually do
> > this since we haven't expanded the inode's extra size space in over a
> > decade, and so this only happens in a debugging mount option that
> > syzbot helpfully uses, and not in real life.
>
> I think we would regret removing this if/when we *do* expand the inode
> size. We used this functionality to upgrade filesystems online when
> i_projid was first added and users suddenly wanted to use project quotas.
> If we need some new inode field in the future it will be good to have it.

Or expand extra_isize only when someone tries to set an inode field that
actually requires it? e.g. whenever setting the project id?

--D

> > Also, there's no real point in doing this on the evict path,
> > especially if the inode is about to be released as part of the
> > eviction.
>
> This could check in ext4_orphan_cleanup()->ext4_evict_inode() path
> that this is orphan cleanup with EXT4_ORPHAN_FS and skip the expansion?
> As you write, it doesn't make sense to do that when the file is being
> deleted anyway. Something like the following, which adds unlikely() to
> that branch since it may happen only once or never in the lifetime of
> any inode:
>
> Cheers, Andreas
> ---
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e99306a8f47c..ae48748decc5 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -6481,7 +6490,8 @@ int __ext4_mark_inode_dirty(handle_t *handle,
> if (err)
> goto out;
> - if (EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize)
> + if (unlikely(EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
> + !(sbi->s_mount_state & EXT4_ORPHAN_FS)))
> ext4_try_to_expand_extra_isize(inode, sbi->s_want_extra_isize,
> iloc, handle);
>
>
>
>
>
>