mm/filemap: use filemap_end_dropbehind() for read invalidation

Use the filemap_end_dropbehind() helper rather than calling
folio_unmap_invalidate() directly, as we need to check if the folio has
been redirtied or marked for writeback once the folio lock has been
re-acquired.

Cc: stable@vger.kernel.org
Reported-by: Trond Myklebust <trondmy@hammerspace.com>
Fixes: 8026e49b ("mm/filemap: add read support for RWF_DONTCACHE")
Link: https://lore.kernel.org/linux-fsdevel/ba8a9805331ce258a622feaca266b163db681a10.camel@hammerspace.com/


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/20250527133255.452431-3-axboe@kernel.dk


Signed-off-by: Christian Brauner <brauner@kernel.org>