Re: [PATCH v1 2/2] fuse: use iomap helpers to update folio uptodate state

On Wed, Jun 24, 2026 at 12:36 AM Christoph Hellwig <[email protected]> wrote:
>
> On Wed, Jun 24, 2026 at 04:29:54AM +0100, Matthew Wilcox wrote:
> > I believe this to be a bug.  I talked about this a bit as LSFMM, but the
> > fundamental problem is that the folio uptodate flag DOES NOT BELONG TO THE
> > FILESYSTEM (unlike the buffer_head uptodate flag, which definitely does).
> >
> > The MM has a number of sanity checks that make sure we haven't
> > done something awful like mapping a !uptodate folio into userspace.
> > That would potentially leak confidential information to userspace.
> > So when a filesystem clears the uptodate flag, the MM can come along
> > and bring down the whole machine because the mapped folio is now !uptodate.
> >
> > I know we have a terrible writeback error handling story.  But I think
> > the right thing to do is just take out the calls to clear uptodate.
> > In all filesystems.  Darrick took it out of iomap in e9c3a8e820ed but
> > it's time to purge it everywhere.

Sounds good, thanks for looking at this. I'll send a patch to remove
this in fuse.

Thanks,
Joanne