It looks to me like upstream commit robert.anc...@canonical.com-20170213034648-wvwh9evai55o7sm5, first released in lightdm 1.21.4, should adequately address this (by retrying the system call on EINTR). Am cherry-picking this into 1.18.3, will test then tag this bug accordingly.
(Note to other would-be cherry-pickers: the commit depends on an earlier one, michael.te...@canonical.com-20161020085337-efsjna95ma6yio89.)
