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

[Greg KH <gregkh@linuxfoundation.org>]

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>
> Reported-by: Google Big Sleep <big-sleep-vuln-reports+bigsleep-501448199@google.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Jan Kara <jack@suse.cz>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> (cherry picked from commit 615d9bb2ccad42f9e21d837431e401db2e471195)
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  mm/filemap.c  | 3 ++-
>  mm/internal.h | 1 -
>  mm/truncate.c | 6 +++++-
>  3 files changed, 7 insertions(+), 3 deletions(-)

This is odd, it's applying with a ton of fuzz, which puts things in the
wrong functions and breaks the build.  Let me go fix it up by hand...

thanks,

greg k-h