Linux: syncfs(2) should sync all open files

While debugging problem with data not being synced on umount, we've
noticed that even syncfs(2) doesn't help to get the data written
out. It is because it doesn't actually sync any of the live znodes.

Signed-off-by: Pavel Snajdr <[email protected]>

module/os/linux/zfs/zpl_super.c

@@ -109,11 +109,23 @@ zpl_sync_fs(struct super_block *sb, int wait)
 {
 	fstrans_cookie_t cookie;
 	cred_t *cr = CRED();
+	znode_t *zp;
+	zfsvfs_t *zfsvfs = sb->s_fs_info;
 	int error;
 
 	crhold(cr);
 	cookie = spl_fstrans_mark();
-	error = -zfs_sync(sb, wait, cr);
+	mutex_enter(&zfsvfs->z_znodes_lock);
+	for (zp = list_head(&zfsvfs->z_all_znodes); zp;
+	    zp = list_next(&zfsvfs->z_all_znodes, zp)) {
+		if (zp->z_sa_hdl)
+			error = -zfs_fsync(zp, wait, cr);
+		if (error != 0)
+			break;
+	}
+	mutex_exit(&zfsvfs->z_znodes_lock);
+	if (error == 0)
+		error = -zfs_sync(sb, wait, cr);
 	spl_fstrans_unmark(cookie);
 	crfree(cr);
 	ASSERT3S(error, <=, 0);