On Thu, Mar 30, 2017 at 06:20:34PM +0200, Michal Hocko wrote: > On Thu 30-03-17 10:47:52, Jiri Kosina wrote: > > On Tue, 28 Mar 2017, Rafael J. Wysocki wrote: > > > > > > > > we have been chasing the following BUG() triggering during the memory > > > > > > hotremove (remove_memory): > > > > > > ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > > > > > > check_memblock_offlined_cb); > > > > > > if (ret) > > > > > > BUG(); > > > > > > > > > > > > and it took a while to learn that the issue is caused by > > > > > > /sys/firmware/acpi/hotplug/force_remove being enabled. I was really > > > > > > surprised to see such an option because at least for the memory hotplug > > > > > > it cannot work at all. Memory hotplug fails when the memory is still > > > > > > in use. Even if we do not BUG() here enforcing the hotplug operation > > > > > > will lead to problematic behavior later like crash or a silent memory > > > > > > corruption if the memory gets onlined back and reused by somebody else. > > > > > > > > > > > > I am wondering what was the motivation for introducing this behavior and > > > > > > whether there is a way to disallow it for memory hotplug. Or maybe drop > > > > > > it completely. What would break in such a case? > > > > > > > > > > Honestly, I don't remember from the top of my head and I haven't looked at > > > > > that code for several months. > > > > > > > > > > I need some time to recall that. > > > > > > > > Did you have any chance to look into this? > > > > > > Well, yes. > > > > > > It looks like that was added for some people who depended on the old behavior > > > at that time. > > > > > > I guess we can try to drop it and see what happpens. :-) > > > > I'd agree with that; at the same time, udev rule should be submitted to > > systemd folks though. I don't think there is anything existing in this > > area yet (neither do distros ship their own udev rules for this AFAIK). > > Another option would keepint the force_remove knob but make the code be > error handling aware. In other words rather than ignoring offline error > simply propagate it up the chain and do not consider the offline. Would > that be acceptable? Then the only difference between normal mode is that the force_remove mode doesn't send out uevent for not-offline-yet container. I vote to remove force_remove not just it ignored offline error and also it's a acpi global knob that it affect all container devices in system. Thanks a lot! Joey Lee -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
