linux-kernel - Re: [PATCH v7 03/14] fs: provide accessors for ->i

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Message-ID: <aO7NqqB41VYCw4Bh@dread.disaster.area>
Date: Wed, 15 Oct 2025 09:24:42 +1100
From: Dave Chinner <david@...morbit.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Jan Kara <jack@...e.cz>, brauner@...nel.org, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	josef@...icpanda.com, kernel-team@...com, amir73il@...il.com,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-xfs@...r.kernel.org, ceph-devel@...r.kernel.org,
	linux-unionfs@...r.kernel.org
Subject: Re: [PATCH v7 03/14] fs: provide accessors for ->i_state

On Fri, Oct 10, 2025 at 05:51:06PM +0200, Mateusz Guzik wrote:
> On Fri, Oct 10, 2025 at 4:44 PM Jan Kara <jack@...e.cz> wrote:
> >
> > On Thu 09-10-25 09:59:17, Mateusz Guzik wrote:
> > > +static inline void inode_state_set_raw(struct inode *inode,
> > > +                                    enum inode_state_flags_enum flags)
> > > +{
> > > +     WRITE_ONCE(inode->i_state, inode->i_state | flags);
> > > +}
> >
> > I think this shouldn't really exist as it is dangerous to use and if we
> > deal with XFS, nobody will actually need this function.
> >
> 
> That's not strictly true, unless you mean code outside of fs/inode.c
> 
> First, something is still needed to clear out the state in
> inode_init_always_gfp().
> 
> Afterwards there are few spots which further modify it without the
> spinlock held (for example see insert_inode_locked4()).
> 
> My take on the situation is that the current I_NEW et al handling is
> crap and the inode hash api is also crap.

The inode hash implementation is crap, too. The historically poor
scalability characteristics of the VFS inode cache is the primary
reason we've never considered ever trying to port XFS to use it,
even if we ignore all the inode lifecycle issues that would have to
be solved first...

> For starters freshly allocated inodes should not be starting with 0,
> but with I_NEW.

Not all inodes are cached filesystem inodes. e.g. anonymous inodes
are initialised to inode->i_state = I_DIRTY.  pipe inodes also start
at I_DIRTY. socket inodes don't touch i_state at init, so they
essentially init i_state = 0....

IOWs, the initial inode state depends on what the inode is being
used for, and I_NEW is only relevant to inodes that are cached and
can be found before the filesystem has fully initialised the VFS
inode.

-Dave.
-- 
Dave Chinner
david@...morbit.com