On Thu, 12 Feb 2015, Peter Zijlstra wrote: > > > FWIW, the barriers in klp_update_task_universe() and > > > klp_set_universe_goal() look like complete crack, and their comments are > > > seriously deficient. > > > > These particular barriers seem correct to me; you basically need to make > > sure that whenever a thread with TIF_KLP_NEED_UPDATE goes through > > do_notify_resume(), it sees proper universe number to be converted to. > > I'm not seeing how they're going to help with that. > > The comment should describe the data race and how the barriers are > making it not happen. > > putting wmb after a store and rmb before a read doesn't avoid the reader > seeing the old value in any universe I know of.
This is about dependency between klp_universe_goal and TIF_KLP_NEED_UPDATE in threadinfo flags. What is confusing here is that threadinfo flags are not set in klp_set_universe_goal() directly, but in the caller (klp_start_transition()). I fully agree with you that this deserves better comment though. -- Jiri Kosina SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
