fs: move fscrypt keyring destruction to after ->put_super

btrfs has a variety of asynchronous things we do with inodes that can
potentially last until ->put_super, when we shut everything down and
clean up all of our async work.  Due to this we need to move
fscrypt_destroy_keyring() to after ->put_super, otherwise we get
warnings about still having active references on the master key.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Link: https://lore.kernel.org/r/20231227171429.9223-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/super.c

@@ -681,12 +681,6 @@ void generic_shutdown_super(struct super_block *sb)
 		fsnotify_sb_delete(sb);
 		security_sb_delete(sb);
 
-		/*
-		 * Now that all potentially-encrypted inodes have been evicted,
-		 * the fscrypt keyring can be destroyed.
-		 */
-		fscrypt_destroy_keyring(sb);
-
 		if (sb->s_dio_done_wq) {
 			destroy_workqueue(sb->s_dio_done_wq);
 			sb->s_dio_done_wq = NULL;
@@ -695,6 +689,12 @@ void generic_shutdown_super(struct super_block *sb)
 		if (sop->put_super)
 			sop->put_super(sb);
 
+		/*
+		 * Now that all potentially-encrypted inodes have been evicted,
+		 * the fscrypt keyring can be destroyed.
+		 */
+		fscrypt_destroy_keyring(sb);
+
 		if (CHECK_DATA_CORRUPTION(!list_empty(&sb->s_inodes),
 				"VFS: Busy inodes after unmount of %s (%s)",
 				sb->s_id, sb->s_type->name)) {