fuse: use ->reconfigure() instead of ->remount_fs()

s_op->remount_fs() is only called from legacy_reconfigure(), which is not
used after being converted to the new API.

Convert to using ->reconfigure().  This restores the previous behavior of
syncing the filesystem and rejecting MS_MANDLOCK on remount.

Fixes: c30da2e981 ("fuse: convert to use the new mount API")
Cc: <stable@vger.kernel.org> # v5.4
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/inode.c

@@ -121,10 +121,12 @@ static void fuse_evict_inode(struct inode *inode)
 	}
 }
 
-static int fuse_remount_fs(struct super_block *sb, int *flags, char *data)
+static int fuse_reconfigure(struct fs_context *fc)
 {
+	struct super_block *sb = fc->root->d_sb;
+
 	sync_filesystem(sb);
-	if (*flags & SB_MANDLOCK)
+	if (fc->sb_flags & SB_MANDLOCK)
 		return -EINVAL;
 
 	return 0;
@@ -817,7 +819,6 @@ static const struct super_operations fuse_super_operations = {
 	.evict_inode	= fuse_evict_inode,
 	.write_inode	= fuse_write_inode,
 	.drop_inode	= generic_delete_inode,
-	.remount_fs	= fuse_remount_fs,
 	.put_super	= fuse_put_super,
 	.umount_begin	= fuse_umount_begin,
 	.statfs		= fuse_statfs,
@@ -1296,6 +1297,7 @@ static int fuse_get_tree(struct fs_context *fc)
 static const struct fs_context_operations fuse_context_ops = {
 	.free		= fuse_free_fc,
 	.parse_param	= fuse_parse_param,
+	.reconfigure	= fuse_reconfigure,
 	.get_tree	= fuse_get_tree,
 };