On Tue, 2013-08-13 at 14:02 +0200, Rafael J. Wysocki wrote: > On Monday, August 12, 2013 07:02:44 PM Toshi Kani wrote: > > On Tue, 2013-08-13 at 02:45 +0200, Rafael J. Wysocki wrote: > > > On Monday, August 12, 2013 02:40:43 PM Toshi Kani wrote: > > > > On Sun, 2013-08-11 at 23:13 +0200, Rafael J. Wysocki wrote: > > > > > On Thursday, August 08, 2013 04:50:42 PM Toshi Kani wrote: > > > > > > On Fri, 2013-08-09 at 00:12 +0200, Rafael J. Wysocki wrote: > > > > > > > On Thursday, August 08, 2013 11:15:20 AM Toshi Kani wrote: > > > > > > > > On Fri, 2013-08-02 at 18:04 -0600, Toshi Kani wrote: > > > > > > > > > On Sat, 2013-08-03 at 01:43 +0200, Rafael J. Wysocki wrote: > > > > > > > > > > On Friday, August 02, 2013 03:46:15 PM Toshi Kani wrote: > > > > > > > > > > > On Thu, 2013-08-01 at 23:43 +0200, Rafael J. Wysocki wrote: > > > > > > > > : > > > > > > > > > > > I think it fails with -EINVAL at the place with dev_warn(dev, "ACPI > > > > > > > > > > > handle is already set\n"). When two ACPI memory objects associate with > > > > > > > > > > > a same memory block, the bind procedure of the 2nd ACPI memory object > > > > > > > > > > > sees that ACPI_HANDLE(dev) is already set to the 1st ACPI memory object. > > > > > > > > > > > > > > > > > > > > That sound's plausible, but I wonder how we can fix that? > > > > > > > > > > > > > > > > > > > > There's no way for a single physical device to have two different ACPI > > > > > > > > > > "companions". It looks like the memory blocks should be 64 M each in that > > > > > > > > > > case. Or we need to create two child devices for each memory block and > > > > > > > > > > associate each of them with an ACPI object. That would lead to complications > > > > > > > > > > in the user space interface, though. > > > > > > > > > > > > > > > > > > Right. Even bigger issue is that I do not think __add_pages() and > > > > > > > > > __remove_pages() can add / delete a memory chunk that is less than > > > > > > > > > 128MB. 128MB is the granularity of them. So, we may just have to fail > > > > > > > > > this case gracefully. > > > > > > > > > > > > > > > > FYI: I have submitted the patch blow to close this part of the issue... > > > > > > > > > > > > > > > > https://lkml.org/lkml/2013/8/8/396 > > > > > > > > > > > > > > That looks good to me, but we'd still need to make it possible to have > > > > > > > memory blocks smaller than 128 MB ... > > > > > > > > > > > > Do you mean acpi_bind_one() needs to be able to handle such case? If > > > > > > so, it should not be a problem since a memory block device won't be > > > > > > created when add_memory() fails with the change above. So, there is no > > > > > > binding to be done. If you mean add_memory() needs to be able to handle > > > > > > a smaller range, that's quite a tough one unless we make the section > > > > > > size smaller. > > > > > > > > > > > > BTW, when add_memory() fails, the memory hot-add request still succeeds > > > > > > with no driver attached. This seems logical, but the added device is > > > > > > useless when no handler is attached. And it does not allow ejecting the > > > > > > device with no handler. I am not too worry about this since this is a > > > > > > rare case, but it reminded me that the framework won't handle rollback. > > > > > > > > > > I'm not sure which rollback you mean. During removal? > > > > > > > > I meant rollback during hot-add. Ideally, a device should be either > > > > added in usable state (success) or failed back to the original state > > > > (rollback). Added in un-usable state is not really a success for users, > > > > and creates an odd state to deal with. But it is still a LOT better > > > > than crashing the system. So, I think this outcome is reasonable on > > > > this framework because adding rollback at this point will complicate the > > > > things unnecessarily. > > > > > > > > > There are two slight problems here in my view. First, even if the device > > > > > cannot be ejected directly, it still will be removed when its parent is > > > > > ejected, so it may be more consistent to just allow everything to be ejected > > > > > regardless of whether or not it has a scan handler. > > > > > > > > Agreed. > > > > > > > > > Second, I guess the > > > > > removal is undesirable for memory devices for which the registration of the > > > > > scan handler failed, so it would be good to fail the "offline" of such devices > > > > > regardless of how we get there. That's why I thought it would be good to have > > > > > an "offline disabled" flag in struct acpi_device. > > > > > > > > I see. But when attach() failed, the memory device may not be used by > > > > the kernel. So, I think it should be safe to remove it. > > > > > > The failure of .attach() need not mean that the memory is not used by the > > > kernel, though, and the ACPI device object is still there and still may > > > be involved in some removal scenarios (through its parent). > > > > As long as .attach() is failed cleanly, which I think is the case for > > the memory handler (if not, we need to fix it), the rest of the kernel > > code may not know what this device is. That is, the ACPI memory handler > > is the only one that knows PNP0C80 is a memory device. So, I do not > > think the memory can be used in such case... > > Yes, it can, if the kernel discovers it during boot before .attach() is first > called. So say this happens and the ACPI memory device object has a parent > with existing _EJ0. > > The memory handler's .attach() fails, so the initial acpi_bus_scan() won't walk > the namespace below the memory device, but it won't return an error code > either (the root device object is always there). The parent of the failed > node is regarded as operational in particular. > > Now, acpi_scan_hot_remove() is called for the parent. Since the memory device > object doesn't have "physical" devices associated with it, > acpi_bus_offline_companions() will ignore it and acpi_scan_hot_remove() will go > for acpi_bus_trim() and straight for _EJ0 for the parent. Splat! > > I agree that this is a corner case, but I wonder if leaving it this way is a > good idea. :-) Oh, I see. In practice, this case is unlikely to happen because add_memory() fails with -EEXIST at the beginning during boot-time, and is essentially a no-op. But I agree with your point that such case may happen and is safer to not allow ejecting a device with no handler. A system crash is much worse than not being able to eject. Thanks, -Toshi -- 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
