On Wednesday, 18 July 2007 16:29, Alan Stern wrote: > On Tue, 17 Jul 2007 david@xxxxxxx wrote: > > > On Tue, 17 Jul 2007, Alan Stern wrote: > > > > > On Tue, 17 Jul 2007 david@xxxxxxx wrote: > > > > > >>> But what about the freezer? The original reason for using kexec was to > > >>> avoid the need for the freezer. With no freezer, while the original > > >>> kernel is busy powering down its devices, user tasks will be free to > > >>> carry out I/O -- which will make the memory snapshot inconsistent with > > >>> the on-disk data structures. > > >> > > >> no, user tasks just don't get scheduled during shutdown. > > > > > > But a user task may be holding a lock which is needed for putting some > > > device into low-power mode. It can't release that lock if it doesn't > > > get scheduled. > > > > then you can't suspend that box. if you schedule it, it could get another > > lock (or another process gets another lock) > > > > if you can't power down or put hardware into low-power mode without the > > approval of userspace, you are in serious trouble. > > You don't seem to appreciate the issues involved here. Part of the > justification for the freezer is that it doesn't need userspace > approval and it freezes tasks at controlled points where they don't > hold any locks. > > Never mind. It seems clear that this approach will suffer the same > drawback as the proposal for removing the freezer from the > suspend-to-RAM pathway. Namely, device drivers will have to be changed > to prevent user I/O requests from proceeding while devices are supposed > to be quiescent or in a low-power state. I agree. > If a driver fails to handle this properly, its device could be > reactivated in order to service a user request before the memory > snapshot is made. This could easily ruin the snapshot. That's why I've been saying for quite some time that we first need to take care of the drivers. :-) IMO we've reached the point at which, whatever we want to do next, the drivers are in the way. Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
