mm/filemap: gate dropbehind invalidate on folio !dirty && !writeback

It's possible for the folio to either get marked for writeback or
redirtied. Add a helper, filemap_end_dropbehind(), which guards the
folio_unmap_invalidate() call behind check for the folio being both
non-dirty and not under writeback AFTER the folio lock has been
acquired. Use this helper folio_end_dropbehind_write().

Cc: stable@vger.kernel.org
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: fb7d3bc41493 ("mm/filemap: drop streaming/uncached pages when writeback completes")
Link: https://lore.kernel.org/linux-fsdevel/20250525083209.GS2023217@ZenIV/
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/mm/filemap.c b/mm/filemap.c
index 7b90cbeb4a1adfe44da53ea76a60ccc2f0e9609d..008a55290f34a90fdbc35588ad628336a1e5db93 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1589,6 +1589,16 @@ int folio_wait_private_2_killable(struct folio *folio)
 }
 EXPORT_SYMBOL(folio_wait_private_2_killable);
 
+static void filemap_end_dropbehind(struct folio *folio)
+{
+       struct address_space *mapping = folio->mapping;
+
+       VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+       if (mapping && !folio_test_writeback(folio) && !folio_test_dirty(folio))
+               folio_unmap_invalidate(mapping, folio, 0);
+}
+
 /*
  * If folio was marked as dropbehind, then pages should be dropped when writeback
  * completes. Do that now. If we fail, it's likely because of a big folio -
@@ -1604,8 +1614,7 @@ static void folio_end_dropbehind_write(struct folio *folio)
         * invalidation in that case.
         */
        if (in_task() && folio_trylock(folio)) {
-               if (folio->mapping)
-                       folio_unmap_invalidate(folio->mapping, folio, 0);
+               filemap_end_dropbehind(folio);
                folio_unlock(folio);
        }
 }