On Wed 29-11-17 09:20:40, Joey Lee wrote: > On Fri, Nov 24, 2017 at 07:17:41PM +0100, Michal Hocko wrote: [...] > > You cannot hotremove memory which is still online. This is what caller > > should enforce. This is too late to handle the failure. At least for > > ACPI. > > > > The logic in acpi_scan_hot_remove() calls memory_subsys_offline(). If > there doesn't have any error returns by memory_subsys_offline, then ACPI > assumes all devices are offlined by subsystem (memory subsystem in this case). yes, that is what I meant by calling it caller responsibility > Then system moves to remove stage, ACPI calls acpi_memory_device_remove(). > Here > > > > I cannot see any need to > > > BUG() in such a case: an error code seems more than sufficient to me. > > > > I do not rememeber details but AFAIR ACPI is in a deferred (kworker) > > context here and cannot simply communicate error code down the road. > > I agree that we should be able to simply return an error but what is the > > actual error condition that might happen here? > > > > Currently acpi_bus_trim() didn't handle any return error. If subsystem > returns error, then ACPI can only interrupt hot-remove process. > > > > This is why this patch removes the BUG() call when the "offline" check > > > fails from the generic code. > > > > As I've said we should simply get rid of BUG rather than move it around. > > > > As I remember that the original BUG() helped us to find out a bug about the > offline state doesn't sync between memblock device with memory state. > Something likes: > mem->dev.offline != (mem->state == MEM_OFFLINE) > > So, the BUG() is useful to capture bug about state sync between device object > and subsystem object. BUG is a fatal condition under many contexts. And therefore not an appropriate error handling. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
