Re: [PATCH v2] ext4: check folio uptodate state in ext4_page_mkwrite()

[Matthew Wilcox]

On Wed, Dec 03, 2025 at 10:46:57AM -0500, Theodore Tso wrote:
> Matthew, as the page cache maintainer, do we actually need this extra
> rigamarole.  Or can we just skip taking the lock before checking to
> see if the folio is uptodate in ext4_page_mkwrite()?

Oh, this triggered a memory.  Looks like you missed my reply in that
thread.  This patch is bogus.  You need to prevent !uptodate folios from
being referenced by the page tables.

https://groups.google.com/g/syzkaller-bugs/c/kjaCOwdrWVg/m/6Li1dROPBQAJ