Re: [PATCH 6.18.y] mm: call ->free_folio() directly in folio_unmap_invalidate()

[Matthew Wilcox <willy@infradead.org>]

On Thu, Apr 23, 2026 at 10:59:49AM +0200, Greg KH wrote:
> On Mon, Apr 20, 2026 at 03:53:43PM +0100, Matthew Wilcox (Oracle) wrote:
> > We can only call filemap_free_folio() if we have a reference to (or hold a
> > lock on) the mapping.  Otherwise, we've already removed the folio from the
> > mapping so it no longer pins the mapping and the mapping can be removed,
> > causing a use-after-free when accessing mapping->a_ops.
> > 
> > Follow the same pattern as __remove_mapping() and load the free_folio
> > function pointer before dropping the lock on the mapping.  That lets us
> > make filemap_free_folio() static as this was the only caller outside
> > filemap.c.
> > 
> > Link: https://lore.kernel.org/20260413184314.3419945-1-willy@infradead.org
> > Fixes: fb7d3bc41493 ("mm/filemap: drop streaming/uncached pages when writeback completes")
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> Wait, I see what's wrong, this function isn't even in 6.18.y, which is
> why when I apply this it has fuzz and blows up.
> 
> So this isn't going to work at all here, did you send the wrong
> backport?

Oh blimey.  Somehow I did the backport to 6.12.y.  Sorry about that;
I'll do 6.18 now.