Re: [PATCH 3/7] iomap: optional zero range dirty folio processing

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Jun 10, 2025 at 08:55:10PM -0700, Christoph Hellwig wrote:
> On Tue, Jun 10, 2025 at 07:55:52AM -0700, Darrick J. Wong wrote:
> > Hrmm.  On closer examination, at least for xfs we've taken i_rwsem and
> > the invalidate_lock so I think it should be the case that you don't need
> > to revalidate.  I think the same locks are held for iomap_unshare_range
> > (mentioned elsewhere in this thread) though it doesn't apply to regular
> > pagecache writes.
> 
> We should document these assumptions, preferable using (lockdep)
> asserts.

Agreed.  I think most of iomap/buffered-io.c wants the caller to hold
i_rwsem in shared mode for reads; i_rwsem in exclusive mode for writes;
and the invalidate lock for page faults.

The big exception iirc is iomap_zero_range where you need to hold
i_rwsem and the mapping invalidate lock, right?

--D