Merge tag 'vfs-6.16-rc2.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs fixes from Christian Brauner:

 - Fix the AT_HANDLE_CONNECTABLE option so filesystems that don't know
   how to decode a connected non-dir dentry fail the request

 - Use repr(transparent) to ensure identical layout between the C and
   Rust implementation of struct file

 - Add a missing xas_pause() into the dax code employing
   wait_entry_unlocked_exclusive()

 - Fix FOP_DONTCACHE which we disabled for v6.15.

   A folio could get redirtied and/or scheduled for writeback after the
   initial dropbehind test. Change the test accordingly to handle these
   cases so we can re-enable FOP_DONTCACHE again

* tag 'vfs-6.16-rc2.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  exportfs: require ->fh_to_parent() to encode connectable file handles
  rust: file: improve safety comments
  rust: file: mark `LocalFile` as `repr(transparent)`
  fs/dax: Fix "don't skip locked entries when scanning entries"
  iomap: don't lose folio dropbehind state for overwrites
  mm/filemap: unify dropbehind flag testing and clearing
  mm/filemap: unify read/write dropbehind naming
  Revert "Disable FOP_DONTCACHE for now due to bugs"
  mm/filemap: use filemap_end_dropbehind() for read invalidation
  mm/filemap: gate dropbehind invalidate on folio !dirty && !writeback

1 files changed, 24 insertions, 15 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 09d005848f0d..48c944e2c163 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1589,13 +1589,30 @@ 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 (folio_test_writeback(folio) || folio_test_dirty(folio))
+		return;
+	if (!folio_test_clear_dropbehind(folio))
+		return;
+	if (mapping)
+		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 -
  * just reset dropbehind for that case and latter completions should invalidate.
  */
-static void folio_end_dropbehind_write(struct folio *folio)
+static void filemap_end_dropbehind_write(struct folio *folio)
 {
+	if (!folio_test_dropbehind(folio))
+		return;
+
 	/*
 	 * Hitting !in_task() should not happen off RWF_DONTCACHE writeback,
 	 * but can happen if normal writeback just happens to find dirty folios
@@ -1604,8 +1621,7 @@ 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);
 	}
 }
@@ -1620,8 +1636,6 @@ static void folio_end_dropbehind_write(struct folio *folio)
  */
 void folio_end_writeback(struct folio *folio)
 {
-	bool folio_dropbehind = false;
-
 	VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
 
 	/*
@@ -1643,14 +1657,11 @@ void folio_end_writeback(struct folio *folio)
 	 * reused before the folio_wake_bit().
 	 */
 	folio_get(folio);
-	if (!folio_test_dirty(folio))
-		folio_dropbehind = folio_test_clear_dropbehind(folio);
 	if (__folio_end_writeback(folio))
 		folio_wake_bit(folio, PG_writeback);
-	acct_reclaim_writeback(folio);
 
-	if (folio_dropbehind)
-		folio_end_dropbehind_write(folio);
+	filemap_end_dropbehind_write(folio);
+	acct_reclaim_writeback(folio);
 	folio_put(folio);
 }
 EXPORT_SYMBOL(folio_end_writeback);
@@ -2635,16 +2646,14 @@ static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
 	return (pos1 >> shift == pos2 >> shift);
 }
 
-static void filemap_end_dropbehind_read(struct address_space *mapping,
-					struct folio *folio)
+static void filemap_end_dropbehind_read(struct folio *folio)
 {
 	if (!folio_test_dropbehind(folio))
 		return;
 	if (folio_test_writeback(folio) || folio_test_dirty(folio))
 		return;
 	if (folio_trylock(folio)) {
-		if (folio_test_clear_dropbehind(folio))
-			folio_unmap_invalidate(mapping, folio, 0);
+		filemap_end_dropbehind(folio);
 		folio_unlock(folio);
 	}
 }
@@ -2765,7 +2774,7 @@ put_folios:
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			struct folio *folio = fbatch.folios[i];
 
-			filemap_end_dropbehind_read(mapping, folio);
+			filemap_end_dropbehind_read(folio);
 			folio_put(folio);
 		}
 		folio_batch_init(&fbatch);